Vibrating monitor

Depending on what monitor you have (most new lcd/plasma models dont have vertical hold) it may have a vertical hold adjustment knob. If you have not already tried adjusting it, turn it all the way clockwise, then all the way counter-clockwise, and then see if you can find a middle ground and slow or stop the jumping.

Another thing it could be is your video adapter, if the above step does not repair it, shut down the computer, unplug the video cable, then plug it in again and secure it tightly with the provided screws. If THAT still doesn't do it, shut down, remove the video card, then make sure the contacts are not damaged and are clean, re-insert the card and secure it properly to the chassis with its screw. Attach the video cable, and turn on the computer.

If none of the above fixes your issue, the last step I would suggest is reinstalling/updating the drivers for the video card, available at your card manufacturers website.

If that doesn't help you, the only way to continue troubleshooting would be to open the device up and service it, which I would strongly advise against if it is a CRT monitor (Glass screen, heavy) as certain components hold strong charges that can seriously harm you and possibly cause death, if you touch the wrong component.

Try changing the screen refresh rate in Desktop -> Properties -> Settings -> Advanced -> Monitor for xp or Desktop -> Personolize -> Display Settings -> Advanced Settings -> Monitor for vista