chris010172 :
Thanks for your suggestion Fyllehund but I know that the router and connections are sound because other computers in the same room are working perfectly. The Dell computer is definitely connected to the internet because the app showing the local temperature flashes on with a correct reading before becoming 'unobtainable'. I'm beginning to think that maybe it's a virus causing the problem. My Avira virus checker doesn't think there are any on board , but then it hasn't been able to update itself since this problem arose.
Try searching your comp with malwarebytes instead, a very good program. malwarebytes.org
You´ll probobly find some with that when anti virus programs wont.