Hi,
Most every machine I remember has a power light inside on the motherboard somewhere, but there may be some that do not..
If you are getting the Acer screen, you have at least some power, but there are multiple connections..
Some are 12 volt, some 5 volt, and some I think 3 volt..
Even if they are working, they may not have the correct voltage or current flow.. That is something that is very difficult to determine..