Windows 7 boot very very slow (30 min)

I'm using PGP v.10.3.0 (Symantec Encryption Desktop) on my Lenovo Thinkpad W510 (with 14GB RAM and two 500GB Toshiba HD) with Windows Professional 7 SP1 (64-bit). I encrypted all my disks many months ago when I used the previous PGP version.

Now I noticed that - probably whenever installing any Windows update to the operating system - in some cases (it happend 4 times) if I restart the computer the boot process is extremely slow (about 30 minutes!) with the Windows logo on the black background and the disk led blinking...

Is this a known problem? How solving it?

Thanks