EDIT: im now also seeing GFX corruption, im beginning to suspect faulty caps
This could also be a sign of a failing Agnus depending on what it looks like. I've seen those go bad that way before. Also when an Amiga floppy decides to go bad, it can go quickly. Do you have a cleaning floppy or another Amiga you can try it in?
Also try formating new disk and copying some files back and forth. It could be you've just scratched up some of the old disks. That can happen in a blink. It worked fine this time... the next time you try it, it's gone for good.
Plaz