The order you boot the laptop and select the input on the TV will affect how they both "handshake" with each other.
Sometimes you have to select the input on the TV and then boot the laptop.
Sometimes you wait until the laptop is booted and then select the input on the TV that the laptop is connected to.
If it doesn't work at first then try changing the input on the TV to an active source, wait for the picture to comeback, and then switch back to the laptop.
You may have to wait 8-10 seconds way before you get a picture on the TV.
Then you can designate the TV as your 2nd display and change any settings to optimize for the TV (video resolution, etc).
I use a laptop with a video projector and the order sometimes changes for no apparent...