Memory stick not recognized...was working previously...help?

If your stick is not recognised in any computer, then you will not be able to access them. You do have backups elsewhere I hope. Try a few more computers, preferably standalone rather than networked ones in case the school has applied something. It is a bit strange that two sticks have exhibited the same problem. Try someone else's memory stick and if that works, and your doesn't then it looks bad. The one you said warms up may be a red herring, I had one like that but it still worked.