Monitor Troubles

I will be running an application or doing work of some kind and after a half an hour the display will shut off and yet the power light is still on. After a couple of minutes the monitor will come back on but at a smaller size. But if I just leave the monitor running with out opening apps or anything then it will run without being shut off. Is it possible that it is the s3trio 32/64 video adapter or is there a resistor in the monitor that is gone that may be causing this?