Hi, i have this acer. hi, i have this acer 1912 19" lcd monitor, it won't turn on

Question

hi, i have this acer 1912 19" lcd monitor, it won't turn on (actually it will turn on if i wait for a few hours). if i unplug the vga cable and press the power button, it will display "acer "and then "no signal" then goes to standby(orange light). but if the vga cable is plugged in and i turn it on then it will display "acer" and then nothing, and i have to wait for hours for it to be back to normal. any suggestions please