Bitlocker doesn't encrypt my disk

Hello,

I have activated Bitlocker on my Vista Ultimate.
The P.C. has restarted and then the "Encrypting..." dialog box
has started. But the percent remains on "0%" and the hard disk is silent
(doesn't work/write/encrypt).

Hardware info: notebook, AMD Turion 64 with NVidia nForce(tm) RAID Class
Controller. Two 7,200 rpm RAID 1 drivers.

Any suggestion?

Urgent.

Thank you.