WinXP invalid after reinstall

Ok, so My dad has a hand-me-down eMachines T3830 PC with WinXP home.
He got a nasty virus and I had to reinstall Windows from the restore partition of the HDD.
Problem is now it's asking for the product key, but the one that comes up in the validation window when I try to activate it is incorrect, as is the one that's slapped on the side of the tower.
Problem HERE is that the one that's on the tower says Windows XP professional. That's obviously not the right key. I don't remember the last install being Professional, but regardless, the original installation was Home.

So..my main question, after this tirade, is will the configuration of the hardware or the presence of non-original hardware completely invalidate a legitimate partition-based re installation of Windows? Tirade explaining why follows...

My main point of concern is that there was a large HDD as the master (on which the previous install of WinXP was located) and then on the slave was a smaller HDD on which was a regular partition and the restore partition. I completely formatted the larger master HDD and the smaller non-restore partition on the slave HDD and then switched them (yes, I changed the jumpers too) because I've always seen the restore partition on the main HDD on other models of this brand (and I assumed because of this tower's age it didn't even include an extra HDD, but without both of them in either configuration, the computer wouldn't even get past POST). I wonder if an improper hardware configuration would invalidate windows, as there was also a PCI sound card installed during the previous installation and I had experience with another brand of PC not even finishing setup because of a missing 56k modem.