It sounds like the controller is alive but there is a corruption in the returned json data. To verify, you can try:
http://x.x.x.x/ja?pw=yyyyy
where x.x.x.x is your OpenSprinkler’s IP address (with :port if you use a port different than 80), yyyyy is the md5 hash of your device password. You can use https://www.md5hashgenerator.com/ to generate the hash from your password.
The return should be a long json string. You can paste it to:
http://json.parser.online.fr/
to verify if there is anything invalid.
If something is corrupted you will most likely have to do a factory reset (though, if you know how to use HTTP API, you can issue an HTTP API command to just reset whichever option is corrupted)