Laptop gets internet access, desktop doesn't

Similar to others but seems odd.  Dell laptop accesses home wireless network and internet successfully via Netgear wireless router and supplied cable modem.  Dell Desktop has been OK until today.  Desktop is connected by cable from wireless router (I've tried each of the 4 available slots, but no joy).  Suddenly desktop has no internet access and it can't even 'see' the router (can't log into its set-up page) Laptop still works fine.  If I troubleshoot, I get told that cable modem isn't working, but it MUST be because laptop gets to internet via router via modem!

So, tried running cable direct from modem to desktop, bypassing router entirely, still get same problem, and of course wireless network now gone as router has no feed.  All I can think is that the ethernet has corrupted, but system details suggest all is working properly.

Incidentally, tried setting up desktop using netgear wireless adapter (desktop hasn't got inbuild wireless), and this too doesn't work - it gets good netwrok connection but no internet access, could be a different problem, just infuriating.  Any help REALLY welcome.

Thanks.

If more details about makes and models are required, I can provide that, but any initial thoughts out there?

Bric