Letter "T" only works after reboot

A strange thing happened yesterday. Letter "T" of my desktop keyboard stopped working. Whenever I wanted to type "T" or "t", I had to copy it from somewhere and then paste it. After one day of this I decided to reboot my computer to see if it would help. And it did, now the "T" works again!

So I'm glad that the problem is solved but I have no idea where the problem originated from. Since it's obviously software and not hardware related, could it be a virus/malware? Or is it just a glitch in the matrix?