Occasionally I see networked laser printers (especially HPs) which continually show the "Processing Job" message and stick there indefinitely. Resetting the printer results in the same happening again after a short pause.
Usually this occurs when a computer is sending a job to the printer which contains incorrect Postscript commands causing the printer to crash. Resetting the printer just results in the queued job being re-submitted and the crash happening again. In a situation where many users access the printer and the computers are left running 24 hours this can be tough to fix!
Because the printer logs showed no useful information I simply had to look at all the computers which used the printers and cancel the queued jobs. Note that many users don't know they have a printer queue and may not be aware they are causing the problem.