|The external drive MUST have the power adapter plugged into it's case and the power adapter must be powered and be working properly (it's common for people to damage the cord to the case because they pulled on the cord rather than the plug while unplugging it), AND the USB port you have it plugged into MUST be able to supply the standard max USB spec 500ma. |
USB ports directly connected to the mboard should work fine with it - they can all supply 500ma - other ports may not.
The flash drive (or external drive, or memory card reader) must be plugged into a port it will actually work in.
How to tell if the flash drive (or external drive, or memory card reader) is properly recognized as a hardware device, even if you can't access it's data.
Programs you can try to recover your data, if that's okay.
The most frequent reason people can no longer access the data on a USB flash drive, USB External drive, or a memory card
See Response 2:
You DO NOT format it, then try to retrieve data off of it. You will not be able to rescue some of the data off of it for sure for sure if you do that.
You try everything you can to see if you can get it to work properly FIRST.
It's unlikely but possible that the circuits in the external case are not working properly.
In that case, you need to connect the hard drive internally to a computer to see if that's okay, as a slave or in any case so you are NOT booting from it if it has an operating system installed on it.
According to my experiences, you can't run hard drive manufacturer's diagnostics on the hard drive when it's in the USB connected external case.
Check your hard drive with the manufacturer's diagnostics.
See the latter part of response 1 in this:
(thanks to Dan Penny for this link:)
Hard Drive Diagnostics Tools and Utilities
If you don't have a floppy drive, you can get a CD image diagnostic utility from most hard drive manufacturer's web sites, but obviously you would need to make a burned CD, preferably a CD-R for best compatibilty, on another computer if you need to.
If the hard drive itself tests okay, any data problems found can be fixed, one way or another.
If there's nothing wrong with the data when you connect the hard drive internally to a working computer that has an operating system, then if it doesn't work properly when in the external case, taking into account what I have pointed out, then you need to buy yourself another external enclosure.