I've acquired a mac plus that seems to have some kind of screen problems. First i sometimes turn it on and it makes the startup bong but it doesn't do anything else. Most of the times it just boots normally. The menubar is also marked on the screen even when the computer is off (although I guess that could be because of usage). Also the image shows sometimes a little disturbance (although that could be caused by my monitor besides it).

Any clues? how long have i got? and most important, is the problem fixable?