machine rebooting without warning

I am running KDE and gdm on Debian stable, and uname -a gives Linux darinaris 2.6.8-1-386 #1 Thu Nov 25 04:24:08 UTC 2004 i686 GNU-Linux My hardware is Intel Celeron 800MHz, 256MB RAM, TNT2 AGP M64 32 MB video card from dselect (Debian package management program): x11-common, xserver-xorg 6.8.2.dfsg kdebase-bin, kdebase-data 3.3.2.1sarg gdm 2.6.0.8-1sa

About 5 days ago, my computer started to hard reboot (it was as if I had turned the power off, and back on) without any kind of warning. I would be reading email, or a website, and it just reboots. Mean time to failure is measured in minutes, and not many of them. This has been going on for several days. I have a Windows 98 SE dual-boot, which does not exhibit the same behavior. I played a few hours of a graphics intensive windows game (Warcraft 3), with no reboot or other unusual behavior (for windows). Also, if I do nothing, and just let the system boot to the KDE login screen, it stays up indefinitely. If I login and let it sit, even after doing one or two things, it stays up indefinitely. Reboots only occur when I am actively doing something. Occasionally (30%-40% of the time), the reboot occurs when logging into KDE, while it has the splash screen with the train of 6(?) icons that light up. The icon that it's on when it reboots is around the "initialize system peripherals" and "loading desktop" icons. I am writing this post in nano from recovery mode (no X), and it seems to be stable. Also, the delay between when the login screen goes away and when the splash screen comes up seems to be somewhat longer than normal. Finally, on about 15-20% of reboots, ESC does not work to skip the bootup memory test.

On the off chance that my wireless keyboard-mouse has something to do with this, I replaced them both with new ones. Several times a reboot seemed to be caused by clicking the mouse, and combined with the ESC not working symptom, I thought it might be worth a try, but no change. It seems to me now that something got broken in X or KDE somehow, and I'm not sure how to proceed. If someone could mention how to get more information to solve this, I would greatly appreciate it. After this post I will take a crack at logs, but I have not had much success historically making much sense of them. If I can post some other helpful information, please let me know.

-Steve