When You upgrade a computer to Windows Vista or Windows 7 Beta, or install Windows Vista Service Pack, and after a restart, the computers CD/DVD drive no longer works as expected, or it says driver is not digitally signed, you will have to remove the affected filter drivers.

To do this, follow these steps:

1. Open Registry for editing (Regedit.exe).
2. Locate, and then click the following registry sub key:

   HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Class\{4D36E965-E325-11CE-BFC1-08002BE10318}

   Caution
   To make sure that you are in the appropriate registry sub key, make sure that the Default data value is DVD/CD-ROM and the Class data value is CDROM.

   

3. In the right pane, right-click UpperFilters, and then click Delete.
4. Click Yes to confirm the removal of the UpperFilters registry entry.
5. Do the same to the LowerFilters
6. Exit Registry Editor, and then restart the computer.

That it, The CD/DVD should now be working as expected.

Source: http://support.microsoft.com/default.aspx/kb/929461/en-us