Problem with activation

Ok, basics of the system are this:

Got ahold of some bad software earlier this week and it damaged one of the
critical files. I have a duel-boot system (Ubuntu Linux on the other boot)
so I used that to back up critical files, then bought a new copy of windows
home (lost the old disk) and repaired the windows partition.

My problem is this: When I try to log in to Windows, the moment I type my
password in and hit enter it brings up the activation window ("Do you want to
activate Windows now"). No matter what I choose, it just goes right back to
the login screen, and I cannot get to the desktop.

Any suggestions on how to fix this?