Sometimes there is loose hardware. You may just have knocked it back into place.
Originally Posted by Holysky
i had that problem yesturday when i was putting my pc together. Everything worked until i popped in a network card. i have no idea why that happened, but i took it out and the resolution was messed up which led to the drivers of my video card. what i reccomend doing is deleteing all the drivers for your graphics card (if you have one) and then reinstall them.
Just because it happened to you, doesn't mean it's the exact same case for him. Try to focus on the main hardware and begin to eliminate it one by one. Since he's using a prebuilt Dell. I doubt he even has a network card, let alone a graphics card. He's probably just using the Ethernet port on the motherboard. Correct me if I'm wrong.