Hi,
I have a Dell Dimension 4500 Desktop, about 4 years old. Yesterday, the computer randomly turned itself off. Now, whenever I start up the computer, it turns itself off about a minute later. By turn off I mean turn off. The computer completely shuts down. When you try and turn it on, it just turns off as soon as Windows XP loads and it gets to the log in screen.
Anyone got an answer?

Two main issues could be the Power Supply itself or a heat issue.

The CPU probably has an automatic shutdown for destructive heat.

You might try cleaning it out first.

Clean the CPU heatsink.

A can of air would be a good idea.

Follow all of Dell's precautions here:

http://support.dell.com/support/edoc...ce.htm#1101572

The section on the "microprocessor" shows the heatsink.

If you are up to it you could also remove the heatsink and clean the old thermal paste and add new.