Sounds like a monitor problem. My current monitor (which is an old 17" CRT) is started to get a kind of "shadow" on the edges of things, and I've seen it before on old CRTs.
It's worth trying a monitor degauss in case something magnetic has done nasty things to it. (Oh, and check that there isn't a fridge magnet stuck to the monitor while you're at it! :-) But more likely is just that your monitor is on its way to the Great Office in the Sky...