First - try it in multiple ports on said computer...
Second - try it in multiple computers - best bet is computers with various operating systems...
Remember - the point here is NOT to make the USB key WORK in a given computer at this point, but to get the data off of it FIRST.
What was said USB stick formatted with? (What operating system was used to format it, what file system was used on it?)
You can get that message from a stick that has been formatted to a file system not natively accessible to Windows as well as with a USB stick that has gotten corrupted/worn out.