I have just bought the xp upgrade disk (currently using windows ME) but when i enter the product key it comes up with the message 'invalid product key'. I have tried some of the options on the microsoft website (disabling antivirus and opening in 'clean boot' mode) to no avail.
Pleas help!

Sam

Did you buy it through a regular dealer, or downloaded it from the internet for 'cheap'?
If the latter, you have most likely been 'done'.

You could try to do a full install (after you made backups of userdata and stuff), incl. formatting etc. and then put in your ME-CD briefly when asked for verification.

I bought it off ebay. It appears to be proper legit packaging, obviously the person i bought it off may have already used it (in which case they lied in their ad!) but I would have assumed the same product key would still be recognised as I cant see how m-soft would know two pc's have used the same key until a complete the registration. My feeling is its a problem with my pc, but would setup know if the product key had already been used by someone else during installation?

The CD is completely neutral, anybody can use it, as long as they have their own CD-key.
It's only when you go online to activate, that M$ may object if the key has been used elsewhere. A phonecall to M$ should clear the situation.

Could it be that you have tried to install XP before you got that CD?
If so, there may be leftovers from that previous install, that now object to the real McCoy.

I've never tried instally xp on my pc until now so that shouldn't be the problem. I will call ms to get another key (hopefully!).
Thanks for your help.