Did the shrimp sit in the tank and decay? If so, for how long?
As to the ammonia being high, I would use FRITZ ZYME Turbo Start to solve that problem. It's not a medication, and it won't hurt your fish. What it will do and what it's been designed to do is to dump loads of beneficial bacteria into your tank, and rid you of high ammonia and nitrite levels. It costs $19.99, but it's worth it. You want to get the ammonia down as fast as possible.