Computer restarts randomly. Please help me!

As stated in the Windows forum:

Hi, I'd like some help with my laptop.

It a dell vostro 1500, Core 2 Duo T7100, 1.8GHz, 2x512MB of RAM, Nvidia GeForce 8600M GT, Windows Vista home basic.

It all started one day when I ran CCleaner. It restarted. I tried again, same result. Then it continued to the point where every time I downloaded something: anything. I backed up everything, and clean-installed vista. Everything running fine, even CCleaner. After re-installing and configuring everything, all fine. Then the next day it restarted again using CCleaner, then downloading. I clean-install again. Same results, all fine. Now it started again! it restarts with CCleaner, and when downloading anything, even when browsing the internet! the only way nothing restarts it's when using safe mode (like I'm doing now).

All I have installed is the usual Winrar, ccleaner, firefox, ... plus my videocard drivers (surely not a problem, because I had been using the same one long before problems started), DirectX 9, and Microsoft Visual C++ 2005 Redistributable. Windows Defender says there are no viruses, Microsoft Memory Diagnostic tool says no memory problems, device manager says both the CPU's are running fine... Please help!

 

Run System Restore. Or before that, try running your OS in safe mode (by pressing F8 when u turn it on) then once it boots up, go to run, and type in "msconfig" and uncheck everything suspicious from "Services" and "Startup" tabs.

Restart on normal mode.

 

Oh, right I forgot, I accidentally deleted the recovery partition on my first clean install, so system restore is not an option.

 

Try the second method, in safe mode - while in it, uninstall everything you don't need/use - uncheck suspicious startup entries and run antivirus