I was faced today by an exception saying that "Farm is unavailable" and the call stack which for sure wasn't useful for diagnosing that type of error.

My solution to this error was straight forward and below are the steps that I've followed:

1. Open run and type services.msc

2. Search for the SQL server instance and in my case I've found that it's not running, so simply start it :)

After that, refresh the page and everything is normal again !