Monitor flickers and won't come back on.?

I have a monitor that doesn't work properly. When I plug it in, it makes a high pitched buzzing noise. About a minute later, it turns off and back on. It isn't able to turn back on and repeatedly turns off and on until I have to unplug it. After a while, I try to plug it back in and the same thing happens. However, sometimes it works completely fine until I turn it off myself. Why does this happen and how can I fix it.