I have a dell dimension 2400, and power wont go on. I opened the side panel to look inside, and yellow power light is on near power supply connector. When I first plugged it in it went on, then when I pressed the \r\non/off button, it shut off, and wouldnt go back on when I pressed it again. what could this problem be.

Does the monitor go out completely, no power? Or just lose a signal? Check ALL cables, AC and Monitor cables. Could be a Graphics adapter issue or Monitor , try another monitor.Your computer has a few miles on it , right? You could buy a PCI Graphics card if the monitor is OK.

YES, Zian it will work....BUT,....................

1) It is a PCI graphics card, and uses a PCI expansion slot.

http://www.tigerdirect.ca/applications/SearchTools/item-details.asp?EdpNo=2898922&CatId=319

The Dell Dimension 2400 Desktop PC's motherboard, has three long white PCI slots,

http://support.dell.com/support/edocs/systems/dim2400/en/sm_en/techov.htm#1105465

http://www.ebay.com/itm/Dell-Dimension-2400-Desktop-Motherboard-System-Main-Board-F5949-K5148-G1548-/190750417467?pt=Motherboards&hash=item2c699c623b

http://en.wikipedia.org/wiki/Conventional_PCI

If one of those long white PCI slots is open, you can use a PCI graphics card.

Concerned that the graphics card uses DDR3 graphics memory, and your computer only uses DDR Sdram ram memory?

Don't be.

The graphics card has it's own processor (Graphics Processing Unit), and graphics memory.
It runs independent of the system resources; the Processor and Ram Memory.

http://en.wikipedia.org/wiki/GPU

The concern is the Power Supply.
Original power supply's maximum rated Wattage is either 200 Watts, or 250 Watts.

The above graphics card requires a minimum system requirement/power supply requirement; of 300 Watts.

I would recommend replacing the Power Supply.
(Especially with it's age, if it is still the same one)

http://www.tigerdirect.ca/applications/SearchTools/item-details.asp?EdpNo=1389575&CatId=1078

ONE thing though..............
Watch the 20-pin ATX main power cable connector, and the wires in it. Be sure they are in the standard place setup.

Check the pinout, and color code of the wires,

1) Dell Dimension 2400 desktop computer, 20-pin ATX main power cable connector pinout,

http://support.dell.com/support/edocs/systems/dim2400/en/sm_en/techov.htm#1105612

2) STANDARD 20-pin ATX main cable connector pinout, and color code of wires; as set by JEDEC,

http://www.playtool.com/pages/psuconnectors/connectors.html#atxmain20

[Be aware that the ATX main power cable, and connector, you get with a new power supply; such as the above, will have a 20 =4-pin ATX main power cable connector,

http://www.playtool.com/pages/psuconnectors/connectors.html#atxmain20plus4

Use the 20-pin connector, tie the 4-pin power cable up out of the way]

For a time period Dell was making the motherboard's main power cable connector - Proprietary.
Meaning they has that motherboard connector wire pinout changed.
Colors of wires were in a different place, than the standard setup by JEDEC.

Orange wires are 3.3 Volts (DC)
Red wires are 5 Volts (DC)
Yellow wires are 12 Volts (DC)
Black wires are Ground wires.

Guess what happens if a 12 Volt Yellow wire, is plugged into where a Black Ground wire is supposed to be?

ZZZZZZzzzzt! Motherboard fries, processor fries, ram memory fries, and graphics card. (If used)

Check the color code of the wires, in the 20-pin ATX main power cable's CONNECTOR, for the Dimension 2400's power supply.

For additional questions please post in a Comment.
Regards,
joecoolvette

You know the power button in the front? If you open the cover to see the insides, there is the HD that is kind of covered by a metal slot (has like holes...). Well, the HD is right next to the power button in the front, but inside.... Here is a picture. The wires are attached to the HD. yup.

You May hev one of two problems, either you towers power suply is broken, or on of the system fans are not working.
Check the power supply fan on boot. If its working check the CPU fan
Regards

Um, unless you are happy soldering VERY finely and under pressure then go for it, but to be honest, you can pick one up for £30-£50 that will have everything you need and more!

change your power supply..

This means that your power supply needs to be replaced.

Here's a link to an ebay post

HI, this is signaling an issue that is concerning the power unit(power supply). this can also be an issue with the mother board as well. you can confirm the actual issue by, inspecting the cooling fan that is on the power unit. if the power unit fan is not running when you push the power button to power up the PC, replace the power supply. if the fan is running, replace the mother board.

If you have no power by pressing the front power button and you have verified that the black connector coming from the power switch on the front is connected properly to the motherboard, then make sure that both connectors from the power supply are connected properly, the main connector and the p4 connector. Reseat both of the connectors to be sure.


If you still have no power and still have the light coming up on the motherboard then I think the motherboard may be bad cause that means something is shorting out the motherboard and not allowing power to go thru it properly.

replace the fuse