My computer is restarting on its own. What is wrong?

My computer restarts by itself several times with in a daily use. The fan is working fine. The guts are clean. My computer is up to date I think. I just put in new memory sticks. It sends me error messages then when I choose the option to send the error report it won't let me. Sends me another error message. I have current antivirus and have ran scans. I don't know what it could be. HELP!!!!

My computer is restarting on its own. What is wrong?download

Could be bad RAM. Run Memtest86.

My computer is restarting on its own. What is wrong?hijackthis

Take all external devices off Camera, printers, thumb drives etc... just monitor keyboard and mouse...you might even try different keyboard or mouse also. If it still reboots after everything is disconnected then

your power supply is whacked or windows is whacked.

Recommend backing up data, reinstall windows XP. If it still happens then it's powersupply.
It would seem that if you had this start happening after installation of the memory, begin there. The next time you get an error message, click and find all the details and print it if you can. Take down the main error message if you cant. Talk to the store where you bought the memory and make sure you have the right kind. I have a dell and this particular model comes with 2 different system options and it depends on what Mhz it operates at what I need to put in it.
Maybe the memory sticks you put in are causing a hardware conflict with your computer. You'll have to find a link to device manager in Control Panel, then check for one there.
It may be a fatal error that is causing the computer to restart. You can easily stop the restart problem by changing your system