MV-8000 not booting from CD or HD

what where the results?

Have you tried updating the MV's OS via USB?

1. Connect the MV-8000 to your computer via a USB cable.
2. Press [DISK/USB].
3. Press [F3 (USB)].
4. Press [F5 (Connect)].
The message “Save Project?” appears.
5. Press [F1 (No)].
On a Mac, the MV-8000’s hard drive appears on the desktop. On a PC, the MV-8000’s hard drive appears inside “My Computer”.
6. Drag the file “MV8000.PRG” to the MV-8000’s hard disk. Do not place it inside any other folder.
7. Once the file has been transferred, eject the MV-8000’s drive from your computer.
On a Mac, drag the MV-8000 hard drive to the trash. On a PC, right-click on the MV-8000 hard drive and select “Eject”.
8. Shut down the MV-8000.
9. While holding [SEQUENCE] and [DISK/USB], turn the MV-8000 back on. Hold the buttons until the
following screen appears:

Roland MV-8000 PRODUCTION STUDIO
** HD Update Mode **

IMPORTANT: Never shut down the MV-8000 while the update is in process.
When the update has been completed, the version number will be displayed and all LEDs will flash.
10. Restart the MV-8000.

That amount of Ram should be perfectly fine. In fact people have had success with 1GB it just doesn't show it.

You didn't by chance try to put an 8800 update on your 8000 did you? Because that would be bad.