So I did the thermal paste thing and left it alone for a little bit.
Tried using it and it's still happening. Screen flickers for a couple of seconds and then turns off - then I have to turn the monitor off and on to get the screen back. Stays on for about two seconds.
I can try it again tomorrow after leaving the paste to sit a little bit.
Here's my original message for anyone just seeing this (accidently deleted it as the screen was turning off).
Windows 7 Ultimate 64bit
not sure of the on board graphics on it right at this moment but I just installed a new Radeon HD 6450 thinking it might fix the problem, so far it's the same.
Issue: One day I turned it on and as soon as I was browsing the screen froze for a moment then went black. There was an error message about display driver failing (forget exactly. It hasn't come up again).
Now it keeps turning off. Flickers for a second then switches off. Monitor stays on but the screen is black.
I re-installed windows and it worked fine for a whole day and evening, no problems but it's back again.