Network Adapter Not Installed

I've recently came on my desktop and i realized that the internet connection was off it had a red X

But it was working fine before? im not sure what happened. Anyways i cannot seem to find the driver to download it nor do i know what it is.

Amd Athlon ii x2 245 processor 2.9ghz
4.00 gb
64 bit
ati radeon 4200
insiprion 570
dell