I'm still unsure what exactly is saying the IP address is invalid. Is it one of the applications?
Does anything work? Can you web surf or send email?
Normally the router (home hub) supplies an IP address to the PC and it's hard to see how it could be invalid. If that failed I would expect an error message saying that it couldn't get an address, not that it had an address but it was invalid.
Try googling for "IP address invalid bt home hub" and see if anything rings a bell. This page has some troubleshooting tips.