Computer freezing suddenly after 15-50 minutes

So my screen freezes and cant move my mouse at that time. it came after i installed my amd bulldozer fx 6100 into my recent build (Msi 890fxa gd 65 board, gskill ripjaws f3-10666CL9D-9GBRL , msi radeon 6870 twinfrozr 3 and some sata 2 WD harddrive. It sometimes happend on my old build where was an amd phenom II x2 565 3.4ghz processor... Now its happening nearly every 15mins or so. After i defrag my 2year old harddrive it comes after 30-60minutes.... Any help? I think its about the processor not being compatible to the memory and motherboard(OR the harddrive being 2years old and sata 2 and nomore in the markets, makes crappy noises even .Because the memory box says "Designed for Intel LGA 1156 platforms / Compatible whit Intel LGA 1155 sandy bridge and amd am3 CPUS.And their website says that the 890fxa gd65 board does not support that memory,but still detects and works in my build. My chipset in the motherboard is AMD am3 and supports am3+.... Got any clue why it freezes?

You might want to take the web site as knowing what they are talking about, and try some different RAM.