The job scheduler will appear to have halted and it will not process any jobs in the queue. The jobs are in Waiting/Scheduled/Processing/Cancelled status but not changing statuses.
Please perform the steps in sequential order in Home > Reports and Jobs > Jobs > Scheduled Jobs
Step 1 - Take the load off the job scheduler
Step 2 - Cancel all jobs in the 'Processing' state.
Step 3 - Run an immediate instance of the Clean User Sessions job.