ACD 23" and GF 6800 GT with PC

Dear friends,

Something strange is happening with me.
I have a Pentium 4 with GF 6800 GT (AGP) and Apple Cinema Display 23".
When I´ve tried turn-on de computer with that configuration, nothing happened. no boot, no BIOS, only the power supply works and processor fan either.
But when I´ve turned-on with two monitors ( the other is a Samsung 755DFG 17") both work very nice (together or each one only).
The point is, I couldn´t use only my ACD 23" with my machine.

Thanks!