A read error on a disk drive or console medium, or a machine
check error, might indicate a hardware malfunction. When a hardware
problem occurs, a question mark (?) usually precedes the error message
that is displayed on the system console terminal. You should then
perform one or both of the following actions:
If the operating
system is loaded into memory but the STARTUP.COM command procedure
does not execute, a software malfunction has probably occurred.
Suspect this condition if a message similar to following message
does not appear:
The OpenVMS system is now executing the system startup procedure.
Perform one or both of the following actions to correct the
situation:
Try again, by repeating the boot procedure.
For instructions, refer to one of the following manuals:
On VAX systems, refer to the most
recent versions of the OpenVMS VAX Upgrade and Installation Manual and
the upgrade and installation supplement for your VAX computer.
On Alpha systems, refer to the HP OpenVMS Alpha Version 7.3-2 Upgrade and Installation Manual.
If you have a removable system disk, replace it with a backup
copy of the system disk. Try to boot the system again.
Leave the system disk in the original drive. Restore
a backup copy of the system disk. For instructions, see
Backing Up and Restoring the System Disk. Try to boot the system again.
HP OpenVMS System Manager's Manual, Volume 1:... 
Starting Up and Shutting Down the System
