How do I fix my wobbly computer screen?

I've been having problems with my monitor wobbling/rippling. Initially we had a flatscreen monitor and that started to wobble, so we hooked up an old compaq and that worked for awhile. Now its really bad. We've moved the computer around (and actually moved to a different house since this started). If I put the computer on standby for a couple hours it gets a little better, but doesn't go away completely. I need a very step by step answer as I'm not very computer savvy! Someone said it might be the video card? How do I check that? Please help.. my eyes are bugging-out!