Desktop froze

[Bill]

Hi,

I am using Mint 21.1 (Vera) with the Mate desktop, running on an I 7 CPU 
and 12 GB of memory.  Recently, I had the desktop freeze up.  At the 
time, I was doing nothing of importance (playing solitaire while waiting 
for an important phone call) and there was nothing that I was running in 
the background.  I was dragging a card to another pile when the drag 
operation just stopped.  The entire desktop stopped.  The mouse cursor 
could move around normally but nothing could be selected.  The keyboard 
also stopped working, so obviously all of the input functions were not 
working.  I could not even select a terminal window to drop down to a 
command prompt or do an orderly shutdown.  The only solution was to hold 
down the power button to force a system shutdown. After a new startup, 
everything worked as it should.

My question is, what happened?  Presumably I could find a clue to what 
happened by looking  at the log files.  Which ones should I look at and 
where are they located.  I do not think it was a hardware problem and 
probably was the Mate desktop.   I want to know what happened and is it 
very serious.  It seems that everything now is OK and I was doing 
nothing of importance and lost no data.

Bill Stanley