Are you using a wireless keyboard? I have had somewhat similar issues in the past when the battery got low on my wireless. Otherwise it sounds like it's time for a new one
Same problem. But with the 'h', 'g' and 'backspace' button. I have a windows 8 laptop. Please help. When i press 'h' - nh6, when i press 'g'- bg5, and 'backspace' -\.