Is the 17R 5720 or did I just get a bad one?

Two weeks ago I ordered a new 17R from Dell. It arrived on Friday after Christmas and I opened the box and fired it up. For about the first 24 hours, everything was fine, but then I started getting a flicker on the lower part of the screen. Over the next few hours, it got progressively worse and finally got to the point I couldn't use it so I called Dell Technical support. They had me run tests and decided it was in the screen or somewhere and dispatched new parts. The installer arrived with the parts on Thursday after New Years and, after some difficulty getting into the machine, installed the parts. Once again, everything worked fine for a few hours, but then small lines started coming across the screen. This time the condition was even worse, and I started having problems with the mouse. I called Dell supprort yesterday and told them it was still bad. They said they'd send me a new computer but so far all I've got from them is the Email they send out about the contact. I'm assuming the computer was either built with a bad part somewhere or that it was bounced around during my shipment, but I'm worried that the replacement may also have problems. Are screen problems common with this model? Everything else seems to be working fine although I did get frequent messages that the wireless connection had been lost. This is not my first Dell. Between my wife and I, we've owned/own at least six laptops and a desktop and have never had problems with any before.