Assuming you are using Window XP, have you tried disabling Auto restart? Right click on My Computer > select Properties > Advance tab. Under Startup and recovery, click on Settings. Under System failure clear the checkmark beside "Automatically restart. Also place a checkmark beside "Write an event to the system log." Click OK > Apply > OK.
If you get a error next time you restart the computer, be sure and post it here.
Also, Next time you have trouble restarting Windows be sure and post any errors in the Event Viewer, even if you have to check from Safe Mode. In either Safe or Normal mode go to Start > All Programs > Control Panel > Administrative tools > Event Viewer. See if any errors have been entered in the System event log at of near the time there was trouble restarting Windows.
first off i'm not 100% sure of my system specs. i bought some parts off a friend and built a media center computer with them. here goes, i have an amd athalon 1.24 with a gig of corsair high performance ram, a antec 420W power supply,a samsung dvd-ram drive, no floppy, i'm unsure about the mobo though, in an antec case with six drives in the case for a total of approx. 2.7 terabytes of storage. all drives are seagate or hitachi. i also have some of the drives connected through splitters because the power supply doesn't have enough connectors. i've already tried to disconnect the drives (all except c:) to see if it was the drives draining too much power from the pwr supply but it still happened. here is the prob.
when i start my pc, sometimes it restarts within 5 seconds, sometimes it goes all the way to the windows startup screen before it restarts. it passes mem chk and all the drives are displayed. sometimes it just shuts down. i've had this problem for around 8 months and it's really dynamic, it changes slightly every time. for the most part i just keep starting the pc until it boots properly and then it works for a day, week, month but the problem always returns. please help.