What kind of problem did you have with it before this happened?
Did you try to turn it on using the button on the TV or with the remote?
Are there any other devices connected to the TV? If they are connected to HDMI then turn those devices on and see if the tv turns on. If not then try removing all cables on the tv and reconnect them.
Also start by trying to reset your TV. Disconnect the power cord from the outlet, then press and hold the power button on the TV (not the remote), for at least 10 seconds. Then wait a few minutes and plug the TV back in and press power once.