Constantly losing network connection

I currently work off an HP Pavilion ze5300. I have had little trouble with it until last fall. Suddenly, the wireless network would not connect, I tried an external wireless card and it connected fine until I rebooted and it would not connect either. After trying every troubleshoot in the world, I wiped out the harddrive and re-sintalled windows. Wireless worked perfectly for 6 months. Now its happening again. It will connect and then randomly every few minutes it cannot connect. I repair and am good for a few minutes and then lose connection again. After a few repairs, it will no longer repair. When I go into properties I see that my WEP key is erased and that the box that says key is provided is checked. So I re-enter the key and I am fine again for about 5 miutes. The light on the wireless connection sometimes is not lit when I am connected and sometimes is lit when I am not. Windows always locates the network, but can't stay connected. I need some ideas... is this a virus? a bad driver??