There seems to be a glitch with the background layer and history in Photoshop. While I've been working on a file it suddenly broke into a bunch of random colours in one square of the image. When I tried hiding different layers to see where the problem was, the colours in the background layer changed and shifted with every layer I clicked on. When I tried opening another blank file the background layer was a huge glitchy mess that seemed to have some pieces of images recently copied, rather than the normal grey and white checkerboard pattern. Help?