Dell E198WFP Flat Panel Monitor

I purchased the Dell Computer and Monitor exactly one year ago. For the past two weeks, I have intermittenly experienced the following problem. After having the computer and monitor on for approximately one hour or so, a flashing occurs every 2-3 seconds or so, as well as a thin, black horizontal line at the bottom of the screen just above the task bar. I have nothing near which would cause interference (microwave, etc) and there are no loose connections which I can see. Does anyone have any idea what the problem could be? If so, how to correct it?

I would suggest trying a different monitor to rule out either the video card or the monitor. If it happens with a different monitor then swap out the video card for a new one.