Hi Houndini Hammy
Do you have a dell computer ?If yes
Out of Warranty Support Program
Dear Customer – Dell has recognized a motherboard component issue that may affect a portion of the OptiPlex™ GX280, GX270 and SX270 desktops. The failure mode may manifest as an intermittent system problem where some users may experience a failure to boot, a thermal shutdown or intermittent lockups when using the affected systems. Users may also notice that capacitors on the system board are bulging. Although not all systems are affected, Dell has implemented a unique program in North America to provide out of warranty coverage for motherboard failures related to the leaking or expanding capacitors on the affected OptiPlex™ GX280, GX270, and SX270 systems. If a desktop computer listed in the "Products Affected" section has a failed motherboard exhibiting expanding or leaking capacitors and is within the time period described below, contact Dell Technical Support to have the motherboard replaced at no charge per Dell's Next Business Day service coverage program. This motherboard replacement program is valid for 5 years from the original date of purchase of the system or January 31, 2008, whichever occurs first. Systems that fall outside the motherboard replacement offer terms may be repaired under Dell's Out of Warranty service program.
Products Affected: SX270 USFF (Ultra Small Form Factor) GX270 SFF, SDT, SMT (All Form Factors - Small Form Factor, Small Desktop, Small-Mini Tower) GX280 - SFF, SDT, SMT (All Form Factors - Small Form Factor, Small Desktop, Small-Mini Tower)
Even if you do not have a Dell I would look at the caps on the mainboard and the cpu fan.
Also found this
I unplug the tower and rip off the side panel. Depress the power switch for about five seconds to bleed off any latent power in the system, pop out the battery and wait a few minutes. Pop the battery back in, button up the tower and plug in the power cord, keyboard and mouse and monitor. Power up the system and it boots. It has done this three times in the last seven or eight months and this routine has fixed it every time.
You have to get into the BIOS and tell it to disable the onboard audio, forget about any floppy drives, and set the clock. It forgets all this information, apparently, when you leave the battery out for a few minutes. I hope this information will be of some buttistance to someone who is having this issue. It took me about a week to find all the information the first time this happened.