Vista Display Problems - No TV Signal on Toshiba

[lost9999]

I have the most annoying problem ever. I use:

Alienware - mod box

P4

Nvidia 7950

1tb HDD

4 gb ram

Toshiba 42in display

Xbox 360 as MCE

When I use my Xbox (Color Stream HD input) to watch tv (MC) my setup works great. No problems. However, when I switch my tv input to the HDMI port (which is where the pc is plugged in) I get a "No TV Signal on my Toshiba. I cant get into the pc at all. After I mess with it, turn off and turn on a few times it eventually gives me the "Safe Mode" screen and then the display pops up. Very annoying! I turned off sleep, away mode and hibernate with no difference.

I have another setup in my bedroom that does the same dang thing.

Alienware - mod box

AMD

ATI Radeon

1tb HDD

4 gb ram

Toshiba 42in display

Xbox 360 as MCE

Any Ideas!!!!