Blue screen if optical drive disconnected

Hi there, I have just built a system running:
Asus p8p67 motherboard
Intel i5 2500k
Ati 6850 graphics car
Windows 7 ultimate x64
8gb ddr3 1333

My issue is, after removing my sata optical drive, the computer blue screens at windows loading screen and restarts. If I connect the optical drive back in, everything works fine.
I have tested this several times and its always the same scenario.
Both my sata3 hdd and normal sata optical drive are connected to the 6G/b ports on the motherboard.
I have installed the latest videocard drivers and all my mboard drivers are installed.

Does anyone know why my computer works fine with the optical drive connected but blue screens if i disconnect it?

Any help would be greatly appreciated.

Thank you

Does anyone have any suggestions, or things i could try?

Thanks