There seems to be an influx of cases lately, where an administrator has either 'lost', or inherited an RMS environment that they don't know the private key password for.
Let me assure you, I don't know it either. You can go to the security tab in your RMS admin console and reset it to a password you know, but before you do this 'BACK UP YOUR SLC AND PUBLISHING CERTIFICATE'.
So...if you get stuck with an environment that you do *not* know the private key password for do *NOT* uninstall RMS, and re-install a new environment without *first* exporting the SLC, and publishing certificate. If you delete everything without backing up these keys, and don't know the private key password ...'I CAN'T HELP YOU!!'. Even if you have a back-up of the database....'I CAN'T HELP YOU!!!'. You will lose all of your data and ...."I CAN'T HELP YOU!!!'.
There is no secret fix, magic command, or ritualistic dance that I can perform to restore your environment, unless you have backed up the database *and* original RMS server. If you didn't you should lay down on the floor and play dead until your boss goes home for the day, and then see if anyone has an older backup of the system hidden somewhere, and if not, some good quality resume paper.
Hopefully I've made the message clear, on the importance of backing up those keys, and outlined your options if you don't heed this advice. :D