How you I get ride of 'frequency out of range' sign on monitor?

I really need help. I was changing the display settings and I think I put the pixel resolution too high and now my monitor is black with a whit box that says frequency out of range!! I tried to start it in safe mode but it does the same thing! Help!?How you I get ride of 'frequency out of range' sign on monitor?
Instead of selecting safe mode after pressing F8, select ';Enable VGA Mode'; and then reset your screen resolution.How you I get ride of 'frequency out of range' sign on monitor?
You need to find a monitor that can actually display those settings and connect your computer to that and change the settings back down to something reasonable.