I'm trying to hook up my Samsung LNT1954H tv as an external display for my aluminum macbook pro. The TV has a vga input on the back, and i have a mini displayport to vga adapter, and the vga cable to go between them. So I hooked it up, and it all fits, but the tv keeps showing "no input devices" when i try to switch the source. I followed the instructions and everything, but it still doesn't work. Any suggestions?