Thanks for your replies. I don't use my mobile near the PC, but the loose connection thing is something I am looking into, the tech who installed the board wasn't the kind of guy who instilled confidence. I checked out the ASUS site, thanks for the link. My board is an A7A266, but I couldn's see this listed on their site, I did take a look at a few message boards with reviews and the general consensus seems to be that it's not a good board. Could this be the problem, would a bad board or bad BIOS cause the kind of popping, wobble affect I an experiencing?
On the point of power supply, a friend suggested getting a power unit with more wattage as the board and CPU have been upgraded, plus a second hard drive added. The monitor runs off its own power supply. The mains supply to the house could be an issue, lights flicker, going to call the company to check to see if it is a clean supply, guess this could cause monitor problems?
Thanks again, this site is just brilliant!