The fax mode is turned off. The phone keeps ringing without the fax mode picking up.

The fax machine will have an auto answer function which is what you need to disable otherwise it will keep trying to pickup calls.

1. Connect the multi-function printer to a phone line. Most printers with fax capability have more than one phone jack, so make sure you are plugged into the right one.
   

2. Turn the printer on and access the start-up menu. Pick an answering mode based on your expected usage of the fax capabilities of your machine (see the next steps for more information about this).
   

3. Put the printer in manual mode if you expect little fax traffic. The manual mode usually requires you to pick up every call that comes to the machine. If you hear the signal for a fax, you push the start button and hang up.
   

4. Choose the automatic mode if you expect a lot of faxes or have a dedicated fax line. In automatic mode, the printer listens to incoming calls and determines whether they are faxes or voice calls. Voice calls get sent on to your phone, and faxes are picked up by the printer.
   

5. Select the number of rings you want your multi-function printer to give you before dropping a call. If you are using the manual mode you may want to go with four or more rings. Two rings should be sufficient in the automatic mode.
   

6. Load paper into the paper tray. Check on the paper level frequently if you receive a lot of faxes.
   

7. Set the desired print quality, and you are ready to receive faxes.
   

Instructions Things You'll Need:

• Phone line
• Multi-function printer

1. Step 1 Connect the multi-function printer to a phone line. Most printers with fax capability have more than one phone jack, so make sure you are plugged into the right one.
   
2. Step 2 Turn the printer on and access the start-up menu. Pick an answering mode based on your expected usage of the fax capabilities of your machine (see the next steps for more information about this).
   
3. Step 3 Put the printer in manual mode if you expect little fax traffic. The manual mode usually requires you to pick up every call that comes to the machine. If you hear the signal for a fax, you push the start button and hang up.
   
4. Step 4 Choose the automatic mode if you expect a lot of faxes or have a dedicated fax line. In automatic mode, the printer listens to incoming calls and determines whether they are faxes or voice calls. Voice calls get sent on to your phone, and faxes are picked up by the printer.
   
5. Step 5 Select the number of rings you want your multi-function printer to give you before dropping a call. If you are using the manual mode you may want to go with four or more rings. Two rings should be sufficient in the automatic mode.
   
6. Step 6 Load paper into the paper tray. Check on the paper level frequently if you receive a lot of faxes.
   
7. Step 7 Set the desired print quality, and you are ready to receive faxes.
   

You should be all set now to receive faxes.

Setting the Ring Delay
The Ring Delay sets the number of times the
MFC rings before it answers in Fax Only or
Fax/Tel mode. If you have extension
phones on the same line as the MFC or
subscribe to the telephone company’s
Distinctive Ring service, keep the Ring Delay
setting of 4.
(See Operation from extension telephones on
page A-4 and Easy Receive on page 4-3.)
1 If it is not illuminated in green, press
(Fax).
2 Press Menu/Set, 2, 1, 1.
3 Press ▲ or ▼ to select how many times
the line rings before the MFC answers
(00 - 04).
Press Menu/Set.
(If you select 00, the line won’t ring at
all.)
4 Press Stop/Exit.
Initial Setup
1.Receive Mode
Current Receive Mode
Fax : Fax Only
F/T : Fax/Tel
TAD : External TAD
Mnl : Manual
Setup Receive
1.Ring Delay

I normaly set all my fax machines on fax only,but I change my incomming ring count to more than 7 rings,but less than 11 rings,this allow you to have time to answer you call before it goes to fax.But you can set it for manual.
Press the "receive mode/resolution button untill it show on the display-manual,fax only or ansering.
Yes you can use the fax and answering machine when you are out of the office.
Set you answering machine to pick up after one ring,the message must not be longer than 15 sec.
If you leave set your receive mode to answering mode

Hope this will help you

Receive Mode Settings Select from the following receive mode options to suit your needs. Once you've decided on which receive mode to use, follow the below instructions to set the receive mode using the operation panel. Receive Mode Setting

1. Press the <FAX> button to enter Fax mode.
   
2. Press <Menu>.
   
3. Press the right or left arrow button to select [Receive mode settings], then press the <OK> button.
   
4. Press the up or down arrow to select the receive mode that best suits your needs, then press <OK>.
   
   

Types of receive mode
Select the receive mode according to your needs.
Receive mode
Purpose
FAX/TEL AUTO SW When you want to receive faxes automatically as well as voice calls. FAX ONLY MODE When you want to receive only faxes automatically with your machine, or have a dedicated telephone line for FAX use only. DRPD When you have subscribed to a DRPD service with your telephone company. MANUAL MODE When you receive mainly voice calls and sometimes faxes, or want to receive faxes manually. ANS.MACHINE MODE When you want to receive voice messages on your answering machine and receive faxes automatically. FAX/TEL auto switch
FAX :
The machine does not ring but will receive the fax automatically. Voice call :
The phone attached to the machine will ring. Pick up the handset to answer the call. Note:

• Ring start timing and Telephone ring length can be specified in FAX/TEL auto switch in the Receive mode settings.
  
• If you want the telephone to ring when it receives a fax, connect a telephone to your machine and enable the Incoming ring settings in RX settings.
  
• The phone attached to the machine may not ring depending on the telephone type you are using.

FAX only
FAX * :
The telephone does not ring. The machine will receive the fax automatically. Voice call :
You will not be able to answer the call. * If you want the telephone to ring, connect the telephone to your machine and enable the Incoming ring settings in RX settings menu.


DRPD
FAX :
Your telephone line will ring according to the ring pattern you have chosen and receive the fax automatically. Voice call :
Your telephone line will ring according to the ring pattern you have chosen. Pick up the handset to answer the call. Note: Specify the FAX pattern in the DRPD: Set FAX ring pat. in RX settings menu.

Manual RX
FAX :
The telephone attached to the machine will ring. Pick up the handset and if you hear a beep tone, press the <Color> or <Black> button on the machine to receive the fax. Voice call :
The telephone attached to the machine will ring. Pick up the handset to answer the call. Note: If you are far from your machine, you can use the remote receiving function to receive faxes. Pick up the handset of the telephone connected to the machine and press 25 (the remote receiving ID).

Ans. machine connect
FAX :
First the answering machine connected to your machine will respond to an incoming call, and then the machine will receive faxes automatically. Voice call :
The answering machine connected to your machine will respond to an incoming call. Note:

• Set the answering machine to answer on the first or second ring.
  
• The entire message should be no longer than 15
  

check the setting in the receive mode button. set it to fax

Its called distintive Ring. This is the instructions from the manual -

VERY IMPORTANT
If you have Voice Mail or a TAD (Telephone Answering Device) and want to keep
one of your phone numbers dedicated only to fax calls, you must leave the fax machine
in MANUAL mode at all times while using the distinctive ring feature. Here’s why:
Manual mode will never pick up a call by itself, since it is «Neutral ». When the fax
machine is in this « neutral » mode, the Distinctive Ring Feature can be activated. The
distinctive ring feature is actually an answering mode. So, do not activate FAX ONLY
mode or FAX /TEL mode while using distinctive ring; otherwise, the fax machine will
answer calls for all the numbers.
Registering the Distinctive Ring Pattern
1 Set the fax machine to MANUAL mode.
2 Press Menu/Set, 0, 1.
3 Press to select DISTINCTIVE:SET?, and then press Menu/Set.
4 Press to select the prestored ring pattern you want to assign, and then press
Menu/Set. (You will hear each pattern as you scroll through the four patterns.)
Be sure to choose the pattern assigned by the Telephone Company.
5 Press Stop/Exit.

and a link to the manual if you need it -
http://static.tigerdirect.com/pdf/brother-IntelliFax-775-Manual.pdf

here is the manual

http://www.retrevo.com/s/brother+2800+fax+manual

please check if the machine is set to correct answering mode i.e. TAD/FAX ?correct it if otherwise. in case it is ok please check whether the DRPD mode may not be switched off ,pls correct it.. HAPPY FAXING HEMANT GROVER