My old monitor seems to be on it's last legs. The picture will randomly fizzle out to a mostly black screen with some garbage lines flickering in the center every now and then, and usually if I wait for a few seconds the picture will come back. Sometimes though if it takes too long, I smack the top of the monitor and that seems to help. What kind of probablem could it be if smacking it will fix it, and how difficult would it be to be permanently fixed?