Acer laptop (Vista) doesn't get pass the black screen with the _ sign.?

This started about 4 days ago. My laptop acts up a lot a couple of months ago January or February I think it stop displaying anything on the screen it has the back light but there's no picture then I let it rest for a month or so when I turned it on it went back to normal but now I have another problem at times it won't get pass the black screen with the _ sign in it. Sometimes it would and it would work fine but when I turn it off then turn it back on it won't work again.