HDTV only detected when turned off (connected via DisplayPort to HDMI)

I tried to connect my LG HDTV (42" LD650) to my MacBook Pro 13" (mid-2010) using a DisplayPort to HDMI adapter. When I plug the cable in, my MacBook's screen flickers every time but the TV is only detected when it is in standby mode. Its status will switch to "No Display Connected" the moment I turn it on.

Here is what System Profiler shows when the TV is in standby mode:

NVIDIA GeForce 320M:

  Chipset Model: NVIDIA GeForce 320M
  Type: GPU
  Bus: PCI
  VRAM (Total): 256 MB
  Vendor: NVIDIA (0x10de)
  Device ID: 0x08a0
  Revision ID: 0x00a2
  ROM Revision: 3533
  Displays:
Color LCD:
  Resolution: 1280 x 800
  Pixel Depth: 32-Bit Color (ARGB8888)
  Main Display: Yes
  Mirror: Off
  Online: Yes
  Built-In: Yes
LG TV:
  Resolution: 1920 x 1080 @ 50 Hz
  Pixel Depth: 32-Bit Color (ARGB8888)
  Mirror: Off
  Online: Yes
  Rotation: Supported
  Television: Yes

I tried the TV and HDMI cable using a Windows PC and it worked instantly.

Is my TV somehow incompatible with the MacBook Pro, or is my adapter faulty, or am I doing something wrong?

While the TV is on standby, try going into System Preferences > Displays Preferences and set your displays to mirror.

I just bought a new adapter (same type/manufacture) and updated to EFI 2.0 - the problem is fixed, now.