Is this a new external drive, or one that was working?
Is this a "store" bought backup drive, or did you buy a HDD and stick it into an enclosuer.
If one of the New Back up drives, was it for a PC or a MAC, if for a MAC that would explain it.
You say you can see it - where, under my computer.
Might try:
.. Right click my computer and select Manage
.. On left side select Disk management.
What does it show? If no partition, can you partition and formate it from there.
I had a simular case with a USB thumbdrive that had been used on a mac. I had to use diskpart cmd to remove the partitions befor I could repartition and format thru windows.