One of many things... has the check engine light come on also? If so, you can pull the codes from the ECM (Autozone or other major parts stores will do it for free). The code/codes will help point in the direction of the failure.

Does this issue go away when you shut down for 5-10 seconds and then restart, only to come back again later? Any more detail you can provide relative to the circumstances under which this happens will help us help you zero in on the problem.