One hour ago, my Mathematica 10.4 StudentEdition, completely crashed, stopped to respond, after I typed 2 letters. For example I wanted to type the command Abs or Exp or Plot and after the second letter it stopped typing and stopped responding. It is really weird, I used task manager, I restarted the PC, afterwards I shut it down and restarted it, but there is no difference. Each time I did that It crashed. This happens only with letters, not with numbers, not with symbols.
It have never happened again, and this period I am using it on a daily basis.
Any idea what kind of trouble is it and how can I solve it?