Sudden freezes cannot find reason

I have bought recently Sapphire Radeon HD5450 1GB DDR3 PCI-E 2.1 graphic card.Put it in my motherboard,reinstalled Windows 7 Ultimate x64,and installed drivers for the graphic card.

From time to time,my computer suddenly freezes.At the "freezed" period (which I suppose can last as long as I let it,because I have tried,and nothing special happens),music stops playing,mouse cursor freezes,unable to CTRL+ALT+DEL to see whats happening.Also,the CPU led at that time is working "on a low level",i.e.constant red light,but not as intense as when system is performing some task.

The only thing I can do,in order to boot successifully,is to turn off machine,unplug it,remove motherboard battery for a few minutes,than put it back,plug in power,and turn it back on.The only changes I make in BIOS afterwards are to disable onboard audio since I have sound card,and set up Smart Q fan monitor for CPU,to lower the noise.

There is nothing in Event Viewer,no crash dump or minidump file to analyze.I just dont know where to start from.

I hope someone has any idea where to start from.

Thx.

you could try using the event viewer go to start in the search box type event viewer. do this first thing after it freezes again then check through the errors and post screenshot. please reply if you want i could do it for u just tell me

nevermind ididnt read the bottom of your problem

how old is this computer?
is it used?
try with safe mode
I got it
update your BIOS

Updating BIOS worked.Thanks so much this was so annoying.

All these days I was in diagnostic startups,to check if the driver is conflicting with any other software.

Thx again!