Remove the KVM device.
Directly attach your monitor, your Sun keyboard and your Sun mouse.
Confirm it can all work properly with those peripherals directly attached.
That would eliminate the computer and the XVR-100 as the root cause.
Then contact the manufacturer of the KVM and get their guidance on making it work.
Many KVM's do not send the proper information
that a compatible keyboard AND mouse are present.
Without all three ( K + V + M ), your console will revert to TTYa or RSC,
whichever one your OBP might have for the default connection for that system.
Thus no output to a screen.
If you need to seek more help from Sun, talk to the OS team, not Hardware Support.
The OS Support team is charged with graphical environment issues.
( ... such as making it visible on a monitor ... )