I have a EMACHINE T6212. Windows XP.

My screen started to vibrate and I thought that I NEED to upgrade my onboard video card. I bought a new video card and insert it into the connector. But my monitor was still plugged to my onboard video card. I turned the machine on, and it was just like before my screen was vibrating. I realized that I forgot to plug my keyboard and I turned off the machine to plug the keyboard and restart again. That was the end of it. My monitor always showed that "No signal" and it is black. I cannot see anything. Only time I was able to see was when my monitor was plugged to my onboard(old) video card, I pressed R key when booting and, recovery option showed to ask me if I WANT to format the machine.

I WOULD really appreciate if anyone can help me with this problem. 'Vibrating screen' can be anything farm a bad monitor, bad CABLE, bad video card, bad PSU and so on. Try another cable and monitor. Or try both monitor and cable on another PC.
Do you have the documentation for  emachine T6212?

If not:
http://support.gateway.com/us/en/emac/product/default.aspx?modelId=1638

Gateway does emachines.