Hard drive does not show up in the devices and removeable storage windows

Is this a self contained unit, or did you buy the HDD and enclouser and put the HDD in the enclouser?

Case 1, self contained unit. Did it come with a AC adaptor, or is it geting power from the USB port. Is this a USB2 or USB3 port. If USB2 and getting power from the USB2 port, it may not be enough power. Usb 2 can only provide a max of 0.5 Amps (2.5 Watts) and this may NOT be enough.

Case 2. If you bought the HDD, it must be initalize prior to use. Can connect to internal sata port, go to windows Disk manager and initialize the HDD, partition it and format.

Not Connecting the Bare HDD (would have to remove it from the encloser) and connecting to an internal sata port on the MB (DO NOT need to mount in a drive bay). would tell you if it is the HDD itself, or a problem with the USB enclosure/USB Port.

We had been using this external drive for a couple of years and it worked beautifully until we broke for summer vacation. Now it is not recognized by any computer.

The first step is to determine if infact it is the HDD, or the electronics of the enclosur.
To detreime you will need to dissasemble and remove the HDD. You can then ether place the HDD in a 2nd enclocure or attach directly to a sata port on the inside of your computer.

Note: if you attach to the inside of your computer and it does not show up in My Computer, double check by looking at disk management and see if it shows up there as a uninitialize HDD, or requires partitioning/Formating (this would indicate the the Boot track has been corrupted.