1. Get to the dead-sergeant prompt
2. Write the following commands:

(VAX) BOOT/R5:10000001 ddcu
(AXP) boot -f 0,1 ddcu

SET /STARTUP OPA0:
SET VAXCLUSTER 0
SET NISCS_LOAD_PEA0 0
SET WRITESYSPARAMS 0
CONTINUE
SET NOON
SPAWN
@SYS$SYSTEM:STARTUP

From this point, you will be in the system with clustering disabled.