|Flash drives don't last forever so it could have died - you could try formatting it (which loses all the data) but even if it works again it is hard to trust it after this sort of problem. |
Best way for the future is to transfer them and check them all out on the new computer. That way if anything goes wrong you have two possible places to find them (the computer and the flash drive). Flash drives are not ideal for backup - an external hard disk is best or even CD/DVD-R.
Always pop back and let us know the outcome - thanks