Problems connecting with Monitor

I have asus g74sx, it has Nvidia Geforce GTX 560M video card. I've recently bought the Benq XL2410T LCD monitor. When I first started it, it was working great. I was able to use DVI to run my games in 3d. I restarted my computer and now DVI works on start up, and will show the screen briefly if I unplug and plug it back in. Also when I plug DVI in my laptop's monitor turns off. So both screens go black when DVI is connected, Vga works find. Anyone know the solution?

Some monitors do not auto detect the connection type so check that your monitor is set to DVI.