You might want to try some general troubleshooting. What happens if you attach that keyboard to another PC? What happens if you attach a different keyboard to your PC? Also, some general maintenance -- have you tried a compressed air duster to blast out any crud? Finally, unlikely, but there are viruses that mess with keyboard input, so check your antivirus software.
have you tried it in safe mode. How does keyboard reacts in safe mode?
If keyboards still behave like this in safe mode then my advice would be to buy a new one. don't spend too much energy on keyboard, they are very cheap nowdays.