Computer freezes

Hello
I’m having huge trouble with my pc.
It freezes after 5 minuts.
I reinstalled my pc from windows 8 to 7 so everything got formatted so it’s definatly hardware…
Any suggestions to test and see what’s wrong?
Aditional information:
After it freeze i have to shut it down and i can start it again and it freezester 5 minuts again so pretty much the same circle hole the time
Update :
dxdiag doesnt see my hd 6870
Update 2 :
Cpu-z detected it but didnt show any mhz clocks so it isnt turned on or is broke i guess
Answer #1
download a program like everest (can be found on wbb) and please provide us with a logfile
Answer #2
jorricks replied: Update :
dxdiag doesnt see my hd 6870
Update 2 :
Cpu-z detected it but didnt show any mhz clocks so it isnt turned on or is broke i guess
I take it you have installed the correct drivers for it ? Does it show OK in Device Manager ?
start > run > devmgmt.msc
If not, try reseating it, and check power cables.
umm, try GPU-Z (not CPU-Z)
http://www.techpowerup.com/gpuz