It depends on the monitor.
If it is an LCD monitor, you may need to replace the backlight lamp. If it is a LED monitor, you should try replacing the power supply. If it is a CRT monitor that has issues with the color display (i.e., red, green, or blue), carefully inspect for debris near these individual components and clean them off if necessary; this may fix your issue depending on what happened to cause white spots in your picture. If your CRT displays whole screen static/scan lines (horizontal or vertical) then check for bad connections inside of the TV unit – if found, try cleaning connectors and resetting their position by pressing them down firmly with a stick figure foot while you turn TV.