reboot problem

I had a machine that exibited this kind of behavior due to having mismatched memory installed. The user installed a second stick of non-parity memory to a machine that had a stick of parity already installed. the machine was capable of using either but not both at the sametime.

I would check for loose connections within the PC, sometimes when a fan comes on a vibration can cause something to ground out. A short is all a reboot button switch creates

My Micron PC with win2k Pro or XPpro did the same thing for months. Obviously past my year to speak to human support....the machine would click off..."try" to reboot. Choosing Safe, Last Known Good all failed. First, blue screens with "Stop" codes of no help to email support. Then the machine would reboot in a perpetual loop canabalizing the file system bit by bit.... never quite getting a foothold so OS could start. They tried the virus answer also..wrong. The WD hard drive passed the diag utility they sent...which I've used for years anyway. That current install did not survive the HD diag. This constant "looping" would/could occur with a fresh clean install of 2k or XP or an install weeks old. No long beeps indicating bad memory. Bios current and configured correct or failsafe. No other tell tale beep codes. They concluded, to throw new system board, Athlon 1 gig TBird CPU and the 256 DDR 2100 Ram at the problem. It worked...with a similar instance happening one time recently and never again. PS I swapped was no help...Left on for over a month the machine was fine...fast and stable. If reboot was needed to complete an install it was 70-30 against that machine would boot thru. Motherboard capacitors, joints all looked fine. When asked, the tech's opinion was the cheep system board and not the Ram or the Cpu. Machine is stable so far but obviously I can never seem to trust it again. Conclude bargain grade Mainboard used by Micron in the configuration I impulse bought couldn't take high duty use. I'll never cut cost on system board and cooling again. PatrickS.

Whenever a computer starts spontaneously rebooting, your first troubleshooting step would be to check the power supply. It's a classic sign of a failing power supply.