My brand-new ultra 20 locks up solid, screen still on, fans running, about once every ten days.
It has 512 RAM, is it just using up all its memory?
I have to cold reboot, the most recent time it happened it was running something pretty important so I sat here hoping it will 'unlock', it has been frozen since 11:03:03 PM since I can read the locked JDS clock.
What is up?

Apps running, mozilla, java media player, one terminal and one zone with a small mysql database, all this under the JDS gui.

oh I cannot ssh into it, nor can I ping it or the zone

Anything in the system log? I had a similar problem with an Ultra 5 and it turned out that the ethernet interface had gone bad.

If you want to see if it is your memory, try running:

# vmstat <interval>

i.e. vmstat 3

This can tell you if your system is running low on resources. Check your "free" field and also your "sr" "pi" and "po".
Also check you syslog messages. /var/adm/messages. Could be you need to start at the prom for update the OBP and then checking your patch levels.

Thank you, I will try your suggestions