Also, even if you’ve rebooted, you could still have some bad state in the HW. A good tech support person will have you shut down completely, wait a few seconds (they’ll ask you to check cables or something), then turn it back on so the capacitors can clear. Rebooting solves 90% of problems, this process solves most of what’s left.
There’s that, but people do lie as well.
Also, even if you’ve rebooted, you could still have some bad state in the HW. A good tech support person will have you shut down completely, wait a few seconds (they’ll ask you to check cables or something), then turn it back on so the capacitors can clear. Rebooting solves 90% of problems, this process solves most of what’s left.