This might need to be in the hardware thread.
If by "jump" you mean it seems to blink out or get smaller then bigger, it might be as simple as poor power (try another power cable to the monitor). It might be as complicated as an internal problem with the monitor. Poor power can come from many things, like a bad cable, or overloaded circuits, or a device on the local grid (edit:meaning your house) which draws a lot of current intermittently (refrigerator, air conditioner, electric water heater, etc.)
Doe the monitor make any sounds when this happens? (popping or clicking).
Please do not open up a monitor to try and fix it. Monitors, like tube televisions, have high-voltage components which can case death.
Is the monitor under warrantee? Make a claim if the power cord replacement trick doesn't fix it.
Other things to consider - video card not seated properly, video cable.