normally if u screw up a bios setting, u see the screen b4 windows boots up, so u can change it back.
if u cannot see the screen, u can reset the cmos, witch is usually done by a jumper switch on the mother bourd, just look for the jumper setting at the manufactures website.
if resetting all the options doesnt bring your picture back, and u didnt change anything else, its most likely a hardware issue.
some one correct me if im rong, but there is no way to brake hardware by changing a setting... unless u overclock a peace of hardware out of its limits.