Please help.....pc locking

What is the exact make and model of the PSU?

What operating system are you using and is it 32 or 64bit?

Does the problem only occur when using Google Chrome or Firefox, or does it happen at other times?

Are all your drivers fully patched and up to date?

Download and install Asus PC Probe II (available through your motherboard support page), use that and provide the temps and voltages of the system when sat at the desktop in Windows.

The above is good advise however probe is not part of the asus suite for that mb. Many of the sabertooth boards do not support probe. Asus thermal radar will monitor temps however I do not think it shows voltages.

Next have you tested your ram with memtest? If not, do so. Let memtest run for a minimum of 1hr to see if you have any errors.
http://memtest.org/
In addition, post the exact ram you have installed. 4gig does not tell us much however 4gig of corsair 1234xxxx ram tells us a lot more.

Will do