Which application are you using?
Which OS version?
If you're using Windows 8 and Photoshop, there is a known bug in Windows itself that causes flashing and bad display results. The solution is usually to update your video card driver from the GPU maker's website. The alternative is setting Photoshop's GPU usage to "Basic" (But you lose some performance and features), or disable the GPU in Photoshop (then you lose several features).