I had my memory stick left in my notepad while I was working, when I got a message saying that there was an unrecognised USB, I took the USB stick out and reinserted it which didn't work, and the computer couldn't find it when I clicked on the icon either. Tried to find it on my PC as well, with no luck. So basically my USB stick seems to have just stopped working...any ideas??

Check your device manager. If the device is listed, uninstall it, restart you computer, and plug it in while computer is idle. Try it, if it doesn't work, sorry.