If this situation happens again run this command
netstat -anb -p tcp | find "TIME_WAIT"
Maybe for some reason all available sockets on your node with SQL server are in waiting state.You may also run this command with /c switch to count sockets in TIME_WAIT state in the loop with a few sec interval and when jobs start failing you would have
at least socket state history.
I periodically clean-up my SQL server by removing past job records from Scheduler database.If I don't do that SQL server responsitivity is gradually getting worst.
Daniel Drypczewski