I know that this might sound harsh. But if you didn't enable the "power failure safety" option when decrypting and you lost power to the disk. The drive may very well be undecryptable. The only other option you could try is to decrypt using a recovery CD, or hook it up to another machine that has PGP Whole Disk Encryption installed. I would make sure that it has the same version of PGP Desktop installed on it before attempting to decrypt.
our recovery images can be downloaded here:
http://www.symantec.com/business/support/index?page=content&id=TECH152604&actp=search&viewlocale=en_US&searchid=1314050687965
Note: DO NOT LET THE MACHINE LOSE POWER WHEN DECRYPTING. YOU MAY WISH TO PUT THE MACHINE ON A BATTERY BACKUP/UPS WHILE DECRYPTING.
If that doesn't work, I'm sorry to say it. But it probably didn't have something written to the disk before loosing power which leaves a pointer telling PGP Desktop where to finish with decryption and what the last i/o operation was before loosing power.
Two things to always keep in mind with WDE:
- Always have a good offline backup
- Always be sure that you have a reliable power source when encrypting/decrypting a disk.