I'd check the RAM or GPU first, as display problems are more often the result of either of these two parts failing. Start by removing one stick of RAM, or replacing the stick of RAM if you've only got one. If nothing changes, move the stick of RAM to a different slot. If still nothing, changes, try using the integrated video chipset (if using a discrete GPU) or conversely, use a discrete GPU (if using the integrated video).
Next, check out the link in my signature, and should you need further assistance, please provide your system specs.