[Elecraft] K3 Stops Transmitting

[Dennis]

In the middle of ARRL DX CW, my K3 stopped transmitting.  It did not 
shut off, it
would go into transmit and there were small flickers in ALC when the 
meter was in
that position, but no power out.  Pushing the TUNE button resulted in 
the display
saying "0 watts".  I played with it for several minutes, was 
unsuccessful in restoring
any transmit capability, so subbed in the replacement rig and kept going.

I brought my K3 home, plugged it in, connected a key and a dummy load, 
and it
transmitted perfectly.  No problems.  I've used it about 3 hours since, 
and there
have been no problems.

First question, what could have happened to result in the no transmit state?
I will be using my K3 again this weekend in a contest.  If the problem
happens again, what possible problems should I be looking for? Loose/
intermittent cable attached to the synthesizer?

Dennis W1UE