Random reboots

Yes well as the name suggests ive been getting alot of random reboots recently (I wouldnt usually post something like this but now im getting them within as little as 10 minute succession or sometimes even less :().

Anyway, Ive googled endlessly to find a solution, and found plenty, but none that worked for me. I dought its overheating, I got a brand new fan less than a month ago, also Ive checked repeatedly and the Processor, Mainboard and Hard Disk temperatures tend to stick within 37-42°C. Also ive run 2 virus and spyware scans, I havnt installed any new programs recently, or downloaded anything suspicious. Ive tryed 3 different power cables, all with no success :(.

Now im stumped. I want to leave a format as a last resort… any ideas?

thanks.