This computer is not running genuine Windows

All's good! Thanks Golden and Noel for your help.

Actually, I spoke to soon...

I've got a problem activating my new windows installation.

I do not have my old product key and neither Dell nor Microsoft can tell me what it is. Apparently I should have used the special Dell Windows7 disk that came with my PC to do the repair install. Dell have told me I need to redo the install with their disk.

When I try to run the Dell version of Win7 it fails the compatibility check because the version of Windows I now have newer than the Dell version.

Any idea what I should do here?

The following issues are preventing Windows from upgrading. Cancel the upgrade, complete each task, and then restart the upgrade to continue.

Your current version of Windows is more recent than the version you are trying to upgrade to. Windows cannot complete the upgrade.

Problem solved. Product Key is under the battery. :)