|"Hp SimpleSave 1TB Hardrive"|
So it IS an external hard drive.
The series is a collaboration between HP and Western Digital. The hard drive is just a simple USB-powered compact external hard drive, much like a My Passport external hard drive, but with HP branding and HP's SimpleSave feature built-in. This SimpleSave software only works with computers running Windows.
Since it last worked properly...
Have you, or is it possible anyone else who had access to it...
- dropped it, or subjected it to a physical jolt
- spilled liquid on it, or exposed it to liquid such as rain, or sprayed it with liquid ?
Hard drive enclosures are relatively cheap to replace if there's something wrong with it.
"USB-powered compact external hard drive,"
It has a laptop sized (2.5") hard drive inside of it. They never have a warranty longer than 3 years. They are much more likely to be damaged if you dropped the external enclosure or subjected it to a physical jolt than desktop sized drives are.
It probably has a SATA hard drive. If so, the SATA data and SATA power sockets on it are exactly the same as on a desktop sized (3.5") drive. The hard drive can be removed and be connected internally to any desktop computer that has a spare SATA data header, and then be tested on that computer.
If there is nothing wrong with the external drive enclosure's circuits or the hard drive inside of it, the most common reason for a problem like yours is you unplugged the external hard drive while Windows was running WITHOUT clicking on the Safely Remove Hardware icon in your Taskbar and choosing to STOP accessing the drive.
When the drive's data area is seen as RAW (un-allocated) usually what the problem is, is the partition table data for the drive is damaged - that damage must be fixed in order for you to be able to access the data on the drive that you know was there before you had this problem. Usually you can use certain data recovery programs, e.g. Recuva, to fix that problem and have access to your data, or most of it, again.
Troubleshooting USB device problems including for flash drives, external drives, memory cards.
See Response 1: