This is gonna sound stupid and random but my PC just keeps rebooting itself. No messages, just reboots. It does seem like a hardware issue. But I'm hoping it's software. HT log is clean as are running processes. Any idea what hardware or OS/software issues this could be? I have also noticed that my Firefox is getting a fair amount of illegal operation messages recently, not sure if it's tied in. I just genuinely don't know where to start but I know it's not spyware or a weird process. I'm running Avast Pro as well so if it is a virus (does seem like one) it's going under that radar. If anyone has any ideas at all...

turn off your automaically restart and then an message will be displayed when the PC crashes right click my computer/system properties/advanced/start up and recovery and then uncheck atomatically restart Post back with the error message Hopefully my advice will help you...Please post back with your results....thanks

Ok, thanks. I've now done that (good idea!!) and now I'll wait to see what the error message in question is and I'll respond here when I see it!

Many things can cause this, My first thought would be heat. Pull a side cover and check for dust and that the fans are spinning OK. Leave the cover off for awhile.

Yeah I find that most of the time this happens due to over heating which means your fans are probably clogged with dust. I clean mine with a can of compressed air regularly.