Computer freeze randomly

[jation]

I have really annoying problem last 30 days. My computer completely freeze randomly in work and I must restart on button. After that computers works fine. This happens sometimes daily, or sometimes after 2-3 days. Maximum once per day.
Also daily and only once between restarts computer freeze for 10-15 seconds sometimes (mostly when opeining calibre or browsing specific web sites) and after that continues to work fine.

Install totally new windows 7 --- freeze again
I check hdd for errors - no errors
Check memory with memtest 4.20 (5 passes) - no errors
Change sata cable --- freeze again
Change sata ports ---- freeze again.
Temperatures are OK ( I5-760: 27-33 on idle, 50-55 when cpu on max)
HDD temperatures also OK (31/34)

Any idea?

Can this happen because bad psu, motherboard or something else?

My system:
CPU - I5-760
Motherboard: H55m-E23
NVIDIa GTS 450
HDD 2TB
HDD 1TB
2xDVDRW

PSU 500W

 

[lovesX79]

video might be over heating or the power supply is not enough Watts for the computer

 

[jation]

I also suspect on CPU.
Temperatures of GPU are also good: 37-39 on idle. I not play games so often. Last play before 2-3 months ago wnen everything work fine. But I remember now when playing my 2 last games (Tomb Raider, Resident Evil 6) my secondary HDD sometimes disappear and back again after restart. Maybe is CPU really bad.

Any way to check my PSU?
Maybe to disconnect both DVD-RWs and secondary HDD to see is there are differences? Or is only way to buy new PSU?

 

[jation]

Fu**ing NVIDIA Drivers freeze computer. Any drivers above 314.07 freeze my computer randomly.

Everything works now fine with 314.07.