projector trouble/video source

I use the Sony vpl-cs5 with my laptop. Works perfectly. I plug it in via USB and it is automatically detected as a human interface device. From there, I can simply switch video modes by pressing F7 to get an image

I tried doing the same thing with my PC. I plugged it in and it was recognized immediately as a human interface device. But I can't figure out how to switch my video out mode so that I get an image from the projector. Thanks in advance for any help.

You might have to add it as a monitor.
Anyway, try Control Panel > Display > Settings

You can choose which monitor to output video to from that screen.
So....