So i just had this exact same problem and worked for hours to find the answer. Space and arrow keys worked, but letters only worked one time. I bought a Lenovo Laptop that came with the program "GuardedID" pre-installed on it. It functions as a decoder for the keys when using flash based games and other things. So when i pressed the key for the first time on the games it would act as a number instead of letters, therefore making it not work. I searched on Lenovo's website in their forums and found the answer to be "delete GuardedID" It has an error in the program. I deleted it and my keys worked immediately in flash games. So if you have a program called "GuardedID" the answer will be to delete it. or if you have a similar program that changes your keys to a different code while on the internet, you need to get rid of it.