You've pretty much lost your data if you can't find your recovery key I'm afraid. The error means the disk information has been corrupted, so probably you installed something else which overwrote the partition gap.
Did you sign up for HP's key storage service? If so your key will be there and they can help you recover, if not, and when it said "Don't loose this information", and you really have lost it, I'm afraid all you can do is use the factory restore CD's and put your machine back to the OOB state (or clear the drive and install Windows again).
Are you sure you lost the decryption key? That would solve your problems pretty easily if you could find it?
Yes, I lost it, but in another 2 notebooks I keep the keys safe.