Firstly, this is not the best place to ask questions on HP's product - you really need to post on their forums. Though your product is based on EEPC 5.2, it's VERY different, and McAfee offer no support for it (as it's a HP product).
Second, you can't access your D drive using a new installation of HPDE on your C drive - even if you use the same password, the keys are very different.
Do you have the USB stick that HPDE created the recovery information on still? If so, there's a possibility you could decrpyt the D partition using it. If not, I'm afraid your data is completely lost.
Thanks for the response. Yesterday I was doing online chat with HP support...but they couldn't give me any specific information. I thought this forum is has good techiee value that why I thought I can discuss it here.
I have the backup created when the encryption is done.