I don't know if you are still having this issue, I'm going over some older posts and came across this one.
I had a similar issue a while back where I couldn't get into my instance either. After many days of frustration, I finally figured out it had to do with the name of the AWS Key being used. I think it either had to do with the space or special character "(" in the name itself. The key I was trying to use was "Servers (us-east)". Once I created a new key and named it "cisco", everything started working. This required me to create a new instance of the CSR but things worked much better after that.
Hope this helps.