If you are using HDMI
1. try booting the PC with the TV on and the correct input selected. Or reverse if that is the way you did it before.
2. Try changing to a different input and back. It may take 10 seconds.
3. Try a different HDMI cable.
4. Try a different HDMI input on the TV.
5. If the PC video resolution is not compatible with the TV you would get an no signal or error message. Change the resolution to match the native resolution of the TV