...almost, but not quite, horizontal, then it sounds like a fault in the CRT tube of your monitor. As repairs to these things can be a bit haphazard - depending on the exact problem - it may be advisable to get a new one. But first, to be sure, find someone who it good at electronics [t.v. repair man?] to take a look at it. Note: there are lots of computer builders out there who can build a p.c. but have little knowledge of grass root electronics.