This page describes using the raspberry pi configured to play video in a loop.
After a bit you should start to see output from booting the machine, after about a minute this will stop and a prompt will appear:
pivideo2 login:
After a few seconds longer the video should start to play.
The raspberry PI uses very little power and can safely be left on for weeks on end, which is what I do with the PIs in my server cabinet. If in doubt this is the safest thing to do from the point of view of the safety of the pi.
As well as the video loop, this PI has:
If you must switch it off please connect to its website and power it down safely.
You can also access the website via an ethernet cable. To do this plug in the cable and go to http://pivideo2:8103
The machine will stop if the usb cable is removed, but it is highly likely that this will corrupt the SD card, so this should only be done in case of emergency. It would be appreciated if you could follow the steps above.