Phone will not power on

It would help to know what model the phone is but the two easiest things to try would be to disconnect the battery and plug it back in or to hold the power and or home button for 20 or so seconds in order to do a hard reset. If these don't work it might be the lcd that is broken. In order to test if the screen is broken plug it in to a computer after trying to turn it on and see if the computer recognizes that it is plugged in. If it does you will most likely need to replace the screen.

Hope this works.