If you go to the properties of the network adapter and select install | add | protocol doesn’t IPv4 show up as an option? This is where you add protocols. If it doesn’t show as an option look here.
This is how I would trouble shoot the problem:
I would start by checking out the error log
Check the cables and cards for damage. Replace them.
Has there been any new additions of software or hardware? If yes remove them.
Have you downloaded updated drivers recently? If yes remove them.
Have you tried system restore to undo system changes that have been made? This is in start menu under accessories – system tools.
Let me know how it goes and if I can be of further assistance.