Far too little detail.
What are your system specs?
Are you seeing high CPU usage in Task Manager even when you aren't actively doing things?
RAM use? Number of open processes that you can account for?
Is it only a graphic artifact, or is it that the computer isn't keeping up with the process...like for instance if you are running a lot of programs, using up all your RAM and CPU utilization and it's stuttering to keep up, or such that weird stuff is displaying, black (or other color) screening and such?
Run a virus scan?