Boot time scan works 5m then blank screen!

[Eddy]

This looks like a hardware issue. Is the system free from dust? (inside the case)

[Undead-Divine-Assassin]

That suggestion by essexboy ^^ or something similar was my guess right from the moment I read the OP.

[Kamykaze]

@essexboy: yes I'm using High Performance profile set to never turn off the monitor and HD. But I think Windows doesn't even come into play. These last tests I didn't even leave the BIOS setup screens. Waited for it to blank looking at the system clock 

This looks like a hardware issue

I believe that too. And I cannot guarantee that it's ever behaved different. This machine is little over 1 yo and I don't remember ever doing a boot time scan (bts) on it 
@Eddy: Dust? What are you thinking about? Overheating? I suppose it could be a little dusty inside. I'll clean it!

Thank you for the help and suggestions. By this time I'm starting to think of a workaround. Maybe I can boot from a CD and scan from there, then again maybe I'll have the same problem.  At least Windows works and I think it's virus free so... let it be? 

[Eddy]

Yes, it sure can be overheating. When cleaning, don't forget to take out and open the psu to remove the dust from inside there too.
Also remove all cards, ram modules and such so you can clean the slots they are in properly.
If this doesn't solve the problem, at least the case is clean and we have ruled out a possible cause for the problem