You need to replace the capacitors in the monitor. If you are not comfortable doing it, you can get someone else to do it. It is not the worst task in the world if you attempt it. Here is a video that looks alright that should give you an idea:
. In terms of the sound, it is either that the volume is turned down really low, or the audio amplification board on the monitor is going out. In the case of the sound being low, there are some knobs by the back of the monitor, and one is labeled volume. Turn that all the way up and see what happens. If that doesn't work, probably the former thing I mentioned. Most of the capacitor kits contain rebuild kits for the audio portion as well. Good luck and welcome to DKF!