In an effort to be more SPECIFICALLY helpful and to hopefully redeem myself to the self appointed, yet strangely not-all-knowing forum police, I offer the following to the OP:
1. If you are using an HDMI cable make sure its a good one. I have a cheap HDMI cable that will not work with my MBP and my Philips TV. My 'better' (read $40) HDMI cable does. Strange but true.
2. Leave your MBP opened. You know, kinda like, I don't know.....oh yeah, like you were giving a presentation on an external display in a bitchin Corporate Board Room without a power supply.
3. Hopefully, you see the Mac desktop image on the Philips screen. This assumes you changed inputs on your TVs remote.
4. Goto system preferences and select sound. Change the output to the HDMI source associated with your TV. If you have problems with this search 'HDMI pass through'.
5. Goto Displays and check the mirror display box.
6. You should see your desktop now.
7. And finally, if you want to use clamshell mode....you will need to plug your MBP into a power supply.
8. I can only hope this helps dislodge the sand from the vaginas of the forum police.
9. This works for me, my MBP, and my Philips TV.