System 7 is compatible with the 7200 Sonnet card so try re-setting the CPU and RAM, if still no joy then try with the original CPU, if it still doesn't work then you could have a faulty card so call Sonnet on Monday.
Sounds like an extension conflict. Go into the extensions manager and turn off some third party extensions. Installing conflict catcher is the answer. I had to do that on a 9600.