I suspect it's a hardware issue, that mimic's a software issue.
1.Do you have a floppy drive? If so, unplug the computer from the AC source of electricity. Open the case. Touch the metal frame of the case to de-static yourself. (Your body contains static. Static will silently fry-out delicate computer parts.) Take the 34 pin flat ribbon interface cable, out of the back of the floppy drive. Take the four pin power connector out also. Now try your computer. If the error message is gone, but Windows still won't boot up, re-start the computer,(Press CTRL, ALT, & Delete keys at SAME time.) Tap the F8 key repeatedly,(Not too fast, not too slow) This should bring you to a window where Safe Mode is one of the options. Use the Up or Down Arrow key to 'highlight' it.(Safe Mode. Not Safe Mode with ya-da, ya-da.) When Safe Mode has fully loaded, do a System Restore. (Start>All Programs>up to Accessories>over and down to System Tools>over and down to System Restore. Tip: Click on the date. It doesn't tell you to take your mouse cursor, and physically click on the date.)
2.You have electrolytic capacitors going bad on your motherboard. These are little barrel shaped 'cans'. They have a plastic sleeve that goes around them, and if you look close, they have an X on top. Sometimes these fail, and leak the electrolytic paste out. This is caused by gas developing inside. Doesn't matter about the age of the computer, just matters whether the capacitors were good in the first place.
A.http://en.wikipedia.org/wiki/Capacitor_plague
B.http://badcaps.net/
http://www.badcaps.net/pages.php?vid=5
These capacitors are used for filters or voltage regulators. Ones around your expansion slots,(ISA, PCI, AGP, PCI-Express are examples of Expansion Slots), are filters. They are in a series circuit, and if one, maybe two goes bad, the expansion slot may still function. It may function, less than, but it may still work. Ones around the processor don't play. They're voltage regulators for the processor. A processor needs steady, 'clean', voltage, and if just one 'cap' goes bad, the processor shuts off.
3.You may have a bad power supply. 80% or so, of the computers I repair are dirty inside. Animal hair/people hair/dust/dirt/spider webs/carpet deodorizer, you name it, has built up inside the computer.
When a power supply's components get a build-up of this stuff, two of the main components will not tolerate it. One, the heatsink inside, two the fan itself. They're both designed, to draw heat away from the power supply components. Once they get coated with this foreign material, the heat factor increases exponentially. Heat=wasted energy.
The power supply tries to put more amperage out, and eventually burns up. (Cap's, wiring, etc.)
When the heatsink/fan on the processor gets dirty, the cpu,(Processor), heats up and shuts off. This is a Fail Safe built-in. (BIOS actually, is the 'one' responsible for shutting the cpu off)
All of the above listed foreign material is also a static 'magnetic'. You know what static will do. The foreign material can also get inside connectors, and cause a make a false circuit, allowing electricity to flow where it isn't supposed to be.
4.Your harddrive is going bad. To check your harddrive you need to do a 'Checkdisk'. This is WinXP's version of 'Scan Disk'.
A.http://support.microsoft.com/kb/315265/en-us
This is a software related issue fix. See if this applies to you.
http://support.microsoft.com/kb/307545/en-us