Press the four button on front panel of monitor simultaneusly and keep pressed untill the unlocked massege will appear when unlocked messege will appear your problem will be solved

This is a technical problem found on PCB (printed circuit board of the Monitor). If you are a qualified electronics technician then you can repair it. If you open the back panel of your monitor you will see the main circuit board where all components are. The soldered side is the side is the one that you have to look at. Usually this problem is caused by dry joints. So the first thing to check on is the dry joints on the vertical oscillator circuit. Check all the capacitors and see if they are not shorted or open. Usually the radial capacitors on the vertical circuit swell at the back, if you see any swollen ones replace them. This should solve the problem. If you are not a technician then refer this to a qualified technician as it can not be done by a lay man.