The order you boot the computer and select the HDMI input that it's connected to affects the "handshake" between the two. This is complicated by the fact that the HDMI output of the PC doesn't turn on right away when you select the input on the TV.
Try selecting the input on the TV and then boot the PC. It might take 8-10 seconds after booting for the TV to show your desktop
Try switching to another active input and back. That sometimes helps.
Try a different HDMI cable. Try a different input on the TV.