|Check the information at this URL: |
Look for the sections on "Conversational Bootstrap on OpenVMS Alpha" and "SYSTARTUP_VMS.COM or such is failing".
Following these instructions should allow you to boot up just far enough to change the code that gets stuck in the loop. For instance, you might submit the mount command to a batch queue instead of doing it in the startup command procedure.
After making the change, reboot normally.