CS5.5 not showing as registered to account--"this serial number has already been registered" error

I've been having errors recently with my copy of InDesign 5.5 not reading files I've saved "for CS4" from my university's CS6 version of the program (I am a graphic design student). I decided it was probably worth an upgrade to CS6 to not have to deal with the errors and get the newer features, but my copy of CS5.5  isn't showing as registered o my account, despite having been installed and registered under my adobe ID when I bought the installation CD.

Not a problem, I still have the CD and serial number. I go to type it in, and get the error "this serial number has already been registered." Adobe's Registration FAQ says to go to Help>Product Registration in the program's menu, but that's not an option in any of the programs I have installed. I'm the first owner of this CD/serial number, so there shouldn't be anyone else with it registered to their account. Is there any way to get the CS5.5 suite that I've purchased registered to my account, despite this error? I'm at a loss.

For anyone's troubleshooting purposes: I'm running the programs on Windows 7 64bit. I've tried deactivating, reactivating, and reinstalling the products, and read through the registration FAQ to no avail. I've tried typing my registration code in the "my products" page, and on the redeem licenses page as well. CS5.5 does not show up in my products, and InDesign 5.5 still won't read my .idml files despite reinstalling and updating.