If you're not experiencing any problems during boot (no lines or odd colors on the screen) then I'd bet it's a driver issue. If you have problems during boot, it's hardware and you're pretty much out of luck until it gets replaced.
Here's what I'd do, and in this order.
Go download the latest drivers for your video card, but DON'T INSTALL THEM YET!
Get Driver Sweeper and blow out all the video drivers on your system (check the ATI and Nvidia boxes, even if you've never had an ATI card in your system. I've found their drivers pop up in the strangest of places!) Then run CCleaner to get rid of all temp files, then use CCleaner to clean the Registry. This makes sure that every single possible trace of the drivers is gone... For good... (This is a good thing!)
Restart into Safe Mode
Run Driver Sweeper again just to make sure it didn't miss any files. If it did, just clean them out and repeat with CCleaner.
Now you may install the drivers you downloaded a few steps ago.
Restart and let the computer boot up normally.
If the problem persists after this, then the card is most likely dying and needs replacement. Nothing I can think of will work as a "band-aid" for a dying video card.
Link to Driver Sweeper -
Scroll about half way down the page and click "I agree" to the T&C to download it.
Link to CCleaner
Hope this helps!