i'll add in a couple of extra pennies for thought...

first off, a good hardware monitoring program is AIDA32. doing a quick google search (keywords "aida32" and "download") should give you a page to DL it from. this is a fantastic FREEWARE program, that will give you lots of info about *all* of the hardware/functioning of your PC.

second, as previously stated, it is likely overheating. i had this issue with a PC recently. want to know the solution that worked for me? i took off the side panel of the computer, got a can of O2 (compressed air), and thoroughly blew off the CPU and heatsink fan. there was A LOT of heavy dust/dirt caked on it, which was keeping the heatsink from running properly (and hence, overheating came into play).

other possible causes of the random rebooting:

- do you have ZoneAlarm? if so, the "True Vector Service" error may appear multiple times in the Event Manager. check that out. if an error with the True Vector Service has happened a lot, shut down ZoneAlarm (temporarily) and delete the ZoneAlarm files with the extension .RDB, and reboot.

- your video card driver may not be fully compatible. it doesn't matter if WinXP says "the device is working properly" in Device Manager. sometimes, a video card drive *appears* to work okay, but for whatever reason, it isn't working right. and this video driver issue can easily come into play if you never installed a driver for your video card and it's an AGP, for instance, and you just let WinXP use its own built-in driver for the video card.

- bad RAM, as has already been mentioned. you might want to google for a program (freeware) called "memtest 86." copy it to a floppy or a CDR(W) disc, and run it overnight. if no errors pop up, your RAM should be fine.

hope this info is of some use.

oh, p.s. AIDA32 will tell you the exact name/model of your Motherboard.

p.p.s. i just re-read the original post, and since there's a laptop involved. it could VERY WELL be, and probably is, an overheating issue. a friend of mine had a laptop (that was 8 months old at the time) that he was about to literally throw away. after some quick research online about the problem (random rebooting, and sometimes the computer not booting up AT ALL), i suggested he open it up and blow it out with compressed air. he didn't feel confident doing that, so he took it to a local computer shop where he lives, and they did it for free. for whatever reason, laptops seem more prone to overheating with a little dust than desktops... my guess is that it's because a laptop doesn't have as much room in the case to begin with, which would mean less space for heat to disperse itself to (and so it hovers around the CPU with nowhere to go).