Downgrading to iTunes 10.3 worked for me too, this confirms it is an iTunes issue (or at least it was for me).
Microsoft Natural Ergonomic 4000 Keyboard (usb)
Latest IntelliType Pro 64-bit
Windows 7 64-bit
After the upgrade to iTunes 10.5 media keys stopped working
Fix:
- Uninstalled iTunes 10.5
- Renamed %userprofile%\music\iTunes to iTunes.old
- Installed iTunes 10.3 (http://support.apple.com/kb/DL1103)
- Copy %userprofile%\music\iTunes.old\iTunes Music to %userprofile%\music\iTunes
- Copy %userprofile%\music\iTunes.old\Album Artwork to %userprofile%\music\iTunes
- Copy %userprofile%\music\iTunes.old\Previous iTunes Libraries\(most recent library file from 10.3 timeframe).itl to %userprofile%\music\iTunes, rename to iTunes Library.itl
- Copy %userprofile%\music\iTunes.old\iTunes Music Library.xml to %userprofile%\music\iTunes
Startup iTunes and your library should be in place, and all music/artwork available to play. Without any further actions my media keys work again both when iTunes is in focus, and when minimized/not in focus.
I guess I just have to remain on iTunes 10.3 indefinitely, as the media keys working is much more important to me than any new iTunes features seem to be..