So I turned off my computer and went shopping and when I came home and turned on my computer everything went as usual but I've lost all my files and programs as if I re-installed Ubuntu. Please help and thanks in advance.
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You need to install ubuntu to your hard drive, or to another external drive in order to keep any files or programs. (Ubuntu will also run faster when installed to a hard drive)
You can also set up a persistent thumb drive. See https://wiki.ubuntu.com/LiveUsbPendrivePersistent/ for more information on that.
If you've already installed Ubuntu to your thumb drive, then it seems you've accidentally booted to a thumb drive. Shut down, remove the thumb drive, and turn your computer back on everything should be back to where it was.