moniter jumping around

[Boondock]

here is the situation. i just upgraded to a new computer about 2 weeks ago. i plugged everything in and turned it on and went through the set up and everything was fine. a few days later i turned it off over night and went i turned it on the next day my screen was bouncing up and down. it did this for about 5 minutes then it stopped. i called tech support and the guy said it's normal for new systems which i did not believe so i called a couple local shops and they said it may be the graphics card. i was quite upset so i took it back and got another computer, same specs. i hooked the 2nd new one up and all was well. i changed my screen resolution from the 1024 by 768 to the lower resolution and it started jumping on me again. when i changed it back to the 1024 by 768 it's fine. i'm thinking it has to be the moniter but i used this very same moniter with my pavillian for 2 years with no problems. it's only 2 years old.

why would it do that at the lower resolution and not the other?
i looked at the connector where it plugs in to the tower and i am missing 2 of those little prongs. could that be the problem?


i'm very frustrated because i hate this resolution and i don't want to buy another moniter. you guys have any ideas of what i can do to switch to the other resolution and have it not bounce on me?

also, it only bounces for a couple minutes, then it gets faster, then it stops and it's fine. if i just restart it it does not do it again but i fi turn it off for any length of time it does it.

thanks for the help.