My System Keeps Shutting Down Randomly!

Ok problem solved .. It was the switch on the surge protector..
IM SO RELIEVED!

just to throw another stick in the mix, upgraded my system about 3 months ago Gigabyte H55MS2H mobo with i3 540 random shutdowns started straight away and i assumed the motherboard, when i spoke to the supplier they suggested it was the psu which was a 600w thermaltake from my old system and had served me well. so i swaped out the power supply with a new 550 thermaltake from another system. the 550 in my system worked fine and solved the problem, the odd thing was that the 600 in the other system also worked fine. interesting? well as i couldnt keep the 550, the 600 went back in and th problem continued, until one day it stoped, iv racked my brain trying to retrace what i could have dont, the only things that stand out are updating the motherboard drivers, replacing the backround picture and updating the bluetooth drivers. now the painful thing is i have done a clean install because i wasnt happy with the amount of crap on there and now my darling problem is back, i have upgraded the drivers and still no fix. i really pains me because i now know that it is a software problem i just dont know how to fix it.