I'm having the same problem with two different ASUS boards (one M2N-SLI and one M4A89GTD): I've connected everything and the systems both power up, but the monitors act as if they're not connected to the computers--there's no change in status on screen, so I can't tell when it hits the BIOS to make a video selection.
On the M2N board, this is even more complicated by the fact that there is no on-board video port--the board requires a graphic card. So I bought a new Radion HD 4650 thinking maybe my previous card was defective. I'm still not seeing any video.
On the M4A, I'm using an EVGA card that had previously worked on the M2N board. This board has both an on-board HDMI and DVI port (I'm using the DVI port), and I'm plugged in to the on-board port until I can get the video card installed. (In both cases, I want to end up with a dual monitor set-up.)
Does anyone have any suggestions for how to proceed?
Also, the M4A build is to end up with a new install of Win7 (it has 16 gigs RAM of G.Skill Ripjaws and an AMD Phenom II 6x processor), while the M2N is supposed to be running WinXP off of 2 gigs of G.Skill RAM and an AMD Athlon 64 X2 processor.