Shut it down completely.
When booting it back up choose the Auto repair boot option from the boot menu after the SUN logo.
If it still won't work after it does its thing:
Select Services > Print from file > Browse and choose Sample Jobs from the dropdown.
See if these jobs will print. If they do, something is wrong with your jobs, possibly the spooler got corrupted, in which case you will need to delete all the jobs on it and start fresh.
Another possibility is that the queue has been accidentally messed with. Try making a new queue via Queue > Queue Manager
Call the new one TEST and give it plain boring simple job properties making sure there is no weirdness anywhere. Then do a test print to that queue and see if it works fine, if it does, either dig through the default queue and figure out what was changed in it by accident, or just create a replacement queue with the queue manager.
If none of that gets you running it would need to be reloaded from scratch, which means a tech call unless you have the license backed up.
