@alex63 ,alex , If board seems worn/damaged, it may be time to replace the key board, below is a link #1 guide to show how to disassemble your laptop to enable the changing of keyboard less then $20.00 in the 2nd link. If you think it could be because of malware or virus you will have to do a scan and get rid of it. You could also try a restore back to a point earlier when all was running well. Good luck. I hope this helped you out, if so let me know by pressing the helpful button.
http://www.irisvista.com/tech/laptops/Toshiba-Satellite-L755-L755D-L750-L750D/dismantle-laptop-1.htm
http://www.laptoppartstore.com/replace--remove-toshiba-satellite-c660-c665-l670-l755-keyboard.html