Rings only 3 times then message

Your model is a phone only, without an answering machine built in. This means that voicemail is provided by your phone service on your line, and that's where you need to adjust the rings before it picks up. The phone itself has nothing to do with it.

You may have to call your service provider for setup instructions because not all systems are the same, but here's how it usually works. Pick up your phone and call your own number to reach your voicemail. When your message starts, press the * button and the system will ask for your pass code (just like when you call to get your messages). Follow the voice prompts to reach the main menu, then mailbox settings, where you'll be able to change the ring count.

If these steps don't work for you, ask your service provider what you need to do.

wen i receive incoming calls there is no ring or message alert

The default security code is "80". If you have not reset that code, you will use 80.
This is all from the manual:
1) Call your telephone number and wait for the system to answer. If the answering system is off, it will answer after about ten rings and sounds a series of beeps.
2) During the greeting or the beeps (if answering system is off), press 0 (zero) and enter your security code within 2 seconds.
3) The answering system announces the current time and the number of messages stored in memory. You hear "To play incoming messages, press zero-two. For help, press one-zero" followed by a beep.
Then the manual lists all the remote commands. If you need those, you can go to uniden.com and download a manual.

See if this works for you.

Remote Operation
When you are away from home, you can operate your answering system with any
touch-tone telephone.Use this function to check for recorded messages, to play or
delete messages, even record a new greeting message.
1) Call your telephone number.
2) During the greeting message, press 0 and enter your PIN code.
3) The answering system announces the current time and the number of messages
stored in memory. Then you hear "To play incoming message, press zero two.
For help, press one zero."
4) You may continue to listen to the voice prompts, or you may select a command
from the following chart:

Command Function
0 then 1 Repeat a Message
0 then 2 Play Incoming Messages
0 then 3 Skip a Message
0 then 4 Delete a Message
0 then 5 Stop Operation
0 then 6 Answering System On
0 then 7 Memo Record/Stop*
0 then 8 Greeting Message Record/Stop*
0 then 9 Answering System Off
1 then 0 Voice Prompts

If you forgot to turn on answering system the directions for that are here:

Turn on the Answering System Remotely
If you have forgotten to turn on your answering system, you can turn it on remotely
from any touch-tone telephone.
1) Call your telephone number.
2) Wait ten rings until the system answers. You hear intermittent beeps.
3) Press 0 and then enter your PIN code. The answering system announces the
number of messages stored in memory. You hear "To play incoming message,
press zero two. For help, press one zero."
4) Press 0 then 6 to turn the answering system On. You hear the outgoing message
and a confirmation tone.
5) Hang up the phone; subsequent calls will be answered by the system.

Go to the base unit.
scroll to the answering machine option.
Under there is a setting for your security key.

you can read what's there, or change it to your own two digit code.

when you call in, during the message, enter that two digit code and it'll go into messages. There's a "toll saver" mode so that the machine answers after two rings instead of 4, so that if you call and it rings 3 times, you know there's no new messages.
Manual:
http://www.uniden.com/pdf/DCT648-2om.pdf

Remotely Operating Your Answering Machine

Call your telephone number and wait for the answering machine to answer. If the answering machine is off, it will answer after about 10 rings and series of beeping sounds.
During the greeting message (or a series of beeps when the answering machine is off), press [0] and enter your PIN code within 2 seconds (see "Setting a Security Code or Personal Identification Number (PIN)" on page 54).
The answering machine announces the current time and the number of messages stored in memory. You hear "To play incoming messages, press zero-two. For help, press one-zero." You will hear a beep.
Enter a remote command within 15 seconds, each command there after must be entered within 2 seconds.

just set the amount of rings higher on the back of the phone and make sure all you old messages are deleted and also make sure its not set to do not disturb

You need to reset the main base unit. Unplug the power from the back of the base. While the power is disconnected, press and hold the delete key while reconnecting the power. Wait for a long beep tone. When the display shows 88 or P, press play button one time. If you have a phone without an answering machine, disconnect the power from the back of the base, press and hold find hs button while reconnecting power.

Here is a link to the pdf format owners manual from Uniden for this phone:

http://www.uniden.com/pdf/TRU8885om.pdf

Remote Operation
You can check, play, or delete messages, even record a new greeting message from a
remote location (when you are away from home, or from another room using a
handset). Additionally, you can turn on or off your answering system remotely.
Remote access away from home
You can operate your answering system from a remote location using any touchtone
telephone.
1) Call your telephone number and wait for the system to answer. If the answering
system is off, it will answer after about 10 rings and sounds a series of beeps.
2) During the greeting message (or a series of beeps when the answering system is
off), press 0 and enter your PIN code within 2 seconds (see "Setting a PIN Code"
on page 25).
3) The answering system announces the current time and the number of messages
stored in memory. You hear "To play incoming messages, press zero-two. For
help, press one-zero." You will hear a beep.
4) Enter a command within 15 seconds, each command there after must be entered
within 2 seconds. You may select a command from the following chart:
* For the Repeat a Message function, press 0 then 1 within about four seconds to
repeat the previous message, or press 0 then 1 after about four seconds to repeat
the current message.
**For the Memo Record and Greeting Message Record functions, the first time you
enter the corresponding command, the phone starts recording. If you want to
stop the recording, press 0 then 7, 8 or 5.
5) After the command has finished, you hear intermittent beeps indicating that the
system is in the command waiting mode. You may enter another command at this
time from the chart above.
6) When you are finished, hang up to exit the system. The answering system
automatically returns to standby.

Command Function Command Function
0 then 1 Repeat a Message* 0 then 6 Answering System On
0 then 2 Playing incoming Messages 0 then 7 Memo Record/Stop**
0 then 3 Skipping a Message 0 then 8 Greeting Message Record/Stop**
0 then 4 Deleting a Message 0 then 9 Answer System Off
0 then 5 Stop Operation 1 then 0 Help

The only reference to flash timing I can find in the manual is shown below for you, also here is link to manual :
I hope it helps !
http://www.uniden.com/products/productdetail.cfm?product=TRU8885-2

If you have Call Waiting service and a call waiting
tone sounds while you are on a call, press talk/flash
on the handset or flash/find hs on the base to accept
the waiting call. There is a short pause, and then you
will hear the new caller. To return to the original
caller, press talk/flash on the handset or flash/find
hs on the base again.

Setting the Ring Time
Ring Time allows you to set the number of rings the caller hears before your
answering system plays the outgoing message. You can set the ring time to answer
after two, four, or six rings. If you enable the Toll Saver (TS), the answering system
picks up after two rings if you have new messages and after four rings if there are
none.
1) Enter the Answ. Setup menu, and then the Ring Time
submenu (see "Entering the Menu" on page 16).
2) Press volume up/down to select a Ring Time (Toll
Saver, 2 Times, 4 Times, or 6 Times).
3) Press the OK soft key. You will hear a confirmation tone.
Setting the Record Time
Record Time sets the duration for recording the incoming messages. You have three
record time options. The options "1 minute" or "4 minutes" set the duration for
recording the incoming messages. "Announce only" answers the call but prevents
the caller from leaving a message.
1) Enter the Answ. Setup menu, and then the Record
Time submenu (see "Entering the Menu" on page 16).
2) Press volume up/down to select Record Time
(1 Minute, 4 Minutes, or Announce Only).
3) Press the OK soft key. You will hear a confirmation tone.