As others have said, John, I think there are too many 'new' bits in your new Dell for the OEM to install. I gather these things work on a points system for CPU/drive/etc etc. I would suggest calling Dell first and asking for re-validation (try "your rubbish machine failed and I have now had to spend £XXX to buy another one of them" sort of thing), then MS if that fails.
Open Office will, I'm sure, do all you want and it is free. I have other options (not for this forum...)