Hybernation Problems I Think...!

I'm not sure whats going on with this PC but until last night it was working fine.

Whats happening is if I walk away from my PC and leave it for a while it seems to go into hibernation mode but won't allow me to come out of it. I have done a "Clean Install" and I am still having the same problem. I have changed my 280 GB Sata Drive for a 500 GB Sata Drive but even with the new HDD I am still getting the same problem.

I am not 100% sure if it is the hibernation mode or the PC is just going to a blank screen. I have also switched off all power settings so my PC should never switch itself into any sleep/hibernation mode. I have used Google and the sevenforums search but can not find anything that will help.

Does anyone have any suggestions...? Also how would I go about turning my hibernation mode off...? If I can switch it off maybe that will tell me if it is hibernation mode or not.

Thanks for any help anyone can give me regarding this issue.

If you need to know anything else just ask. I'll try and do my best to answer any questions.