disappearing cursor/frozen Al-book

[Dr. Trevor J. Hutley]

Three times today this has happened: the cursor has disappeared, and 
the keyboard is totally unresponsive (Char Lock works). 
ALT-APPLE-ESC does nothing,   The Powerbook is completely locked.
I have to do a restart (CTL APL PWR).

I have never seen this before with OS X/Panther.

It seems totally uncharacteristic.

Has anyone seen this?  Any idea what is happening ?

There is no pattern with these occurences.  One was when I was away 
for a few minutes, one was when I was saving a Safari page, and one 
just happened.

Trevor