Graphics card failure, now no Internet.

Ahh, sweet overconfidence. I have had a noisy graphics card for some time. I removed it from my pc today in order to clean the fan etc to see if that would help. The fan didn't clip back on to the card properly (it wasn't my fault!) and so the gpu overheated and failed. Bought a new card to fit (geForce 8400GS). Finally got the drivers for the card to load but device manager tells me that the SM Bus Controller and Other PCI Bridge Device aren't being picked with the result that I have no interweb. Also the machine is running very slowly. Tried rolling back drivers, using motherboard driver disc (MB is Gigabyte GA - K8N - SLI) to no avail. I downloaded drivers from Gigabyte (and then the same ones from nVidia) to an external hard disk which I installed to the desktop pc. Ran these and the yellow question marks disappear. However I still can't connect to the internet. I switched off my modem, waited 3 minutes and fired it up again. Still no joy. If anyone can make a suggestion as to what the problem is I would be very greateful!

(Just started getting "dwwin.exe Bad Image" "c:\WINDOWS\system32\nview.dll is not a valid Windows Image" messages for good measure! Disaster!)