Drivers for NIC not found

I just recently updated to windows 7(32 bit) from xp. The problem is that when i turn my computer off at night and boot it back up later the computer cannot find my Nvidia Nforce networking controllers and I cannot get on the internet without it. The strange thing is when i turn my computer off and unplug it from the wall for a bit then plug it in and boot it back up. It works fine and it finds my Nvidia Nforce networking controllers and i am able to go on the internet. Im not sure if this is a BIOS issue or a NIC issues. Any suggestions would be much appreciated.