Just switch it off at the mains. Or ull the power cable from either the wall or the socket at th eback of the machine.
SHouldn't do any harm.
If you power cycle the TV, it might bring it back to life.
Alternatiely, if it's an HDMI then you could try removing the HDMI cable and re-inserting it at either computer end or TV end.
You can try that also with an older VGA cable but it probably won't recognise the TV, but it's worth a try.
Good luck!