Suddenly started the following:
Starts up, fan runs then 1 beep, fan then goes very fast and another beep then everything immediately shuts down. All of this in about ten seconds.
Yesterday when I first saw it the screen got as far as "computer last shut down unexpectedly. How do you want to restart" etc. Before I could press "safe mode" or any other button, it shut down. Since then it goes thru the above sequence with nothing showing on the monitor at all.