I looked around the forum and found a lot of people have had this problem, but none that matched mine...

Anyway,mine started 2 days ago when the first random reboot happened after I opened up a little program to check the cpu core temperature (coretemp.exe). I've been using it for a week and nothing happened before that.
When the computer rebooted there were no error messages.
Then again a few hours later, I was just surfing the net generally.
Then another reboot and another, and no error messages.

So today I did a full system scan-- AVG and it found this "POTENTIALLY HARMFUL PROGRAM HideExec.BD" " PATH - C:/WINDOWS/SYSTEM32/CMDOW.EXE"

It's in the virus vault.. so I figured if this was the problem, it'll be OK now. But then, another reboot, when I was just browsing the net for 'random rebooting problems.' Haha.

I also did a spyware scan with Outpost Pro-- it came out clean.

Then I checked with "eventvwr.msc" (something I picked up from google) and it showed an error "SERVICE CONTROL MANAGER - FOLLOWING BOOT-START DRIVER FAILED TO LOAD - ASPI32"
this error has occurred several times, even before the random rebooting started.

Phew. Well this is all I have right now. Don't know what's wrong. So if anyone can make some sense out of it, it'll be a big help!

Oh and my system ---

XP Prof SP2
Intel Core(TM) 2 CPU
[email protected] GHz
1.99 GB RAM

You said you change your coretemp.exe so in that case one also it cause some failure on your machine, try to changes on default. In safe mode, and resrtore in last good config. Of your OS second Virus is the one also to force your machine rebooting on an on most especially strong virux.. the last thing if non of the obove try to reinstall your machine in clean boot (NEW ONE) and after that before you begin to do anything on your machine first do it with back-up and enjoy.

This can be AVG itself, There is an option that AVG use to restart the PC when an update is complete. Try this to check whether it helps? Open AVG Control Center > click on update manager > select properties > check update immediately, complete at next computer startup > close dialog box > disable all schedule tasks...