Problem with pixels on edge of canvas

This just kina happened to me out of no where. It was working fine yesterday but when I started up photoshop this morning it's all screwed up. I'm positive its no a setting or something.

Ok, this is my problem. It occurs on all canvas size, small to large. Alot of the pixels across the bottom and up and down the right side basicaly arn't working. For example I take the pencil too and attempt to fill a singel pixel on the bottom of teh canvas. The history records the use of the pencil tool but nothing appears on the canvas. The same is for the marquee tool. If I go a few pixels above the bottom row and select by draging down it will go to the bottom. But if I try to only select the bottom row the marquee outline does not appear and I am told no pixels were selected.

However when I use the fill too those same pixels along the bottom and up the right side are filled. After becoming extreamly agrivated and going nuts with the pencil tool I noticed that if I hold it down and and slide it toward one of the pixels I can eventualy get it, but only after penciling the surring 60 or so pixels.

I have restared photo shop 4 times with no luck. I'm not drawing on the background layer and the color i'm using is not the same as a color below it.

I have no idea what to do.
Any thoughs would be greatly apreciated, thanks.

If anyone ever runs across a problem like this I figured out what it is. All that it was is that snap was turned on. So just turn off and there you go.

What photoshop are u using.