This is quite odd indeed. First of all I would take any back ups now before you do anything that could result in you having to format, better to be prepared incase anything goes awry :)
After you've either imaged or backed up the HDD, you could use some bootable partitioning tools to investigate what the state of your HDD is outside of Windows, because it could be Windows itself who is getting confused. If any app (partition magic for example) outside of Windows thinks its just 1 partition, you can then split it and see if it recovers itself.
I am guessing Windows has gotten itself confused after this decryption (god knows how) and maybe probing the state of the HDD or recovering the MBR via a bootable utility (once you have decrypted) could do the job.
Good luck!