How long a downtime (weeks? months? years?)
The problem could be almost anything; I'm assuming there are no blinking red lights or error codes when you power up the detector. If that checks out, and the lamp *does* ignite, the next thing I would do is to temporarily replace the connecting cable(s). If that doesn't do anything, try to borrow another detector and see if the software will connect the *that*. If it doesn't, try reinstalling the software. If it *does*, then the problem is internal to the detector. You can check the obvious (take the case apart and re-seat any potential loose boards), but it may be time for factory-authorized service.