9010, internal drive not readable via USB

One possibility. Since its a Win 10 formatted disc, its probably formatted for UEFI/GPT  instead of the older NTFS.  If your Win 7 can't read GPT (assuming that's how its formatted) that could be the problem.

GPT or UEFI are not filesystems like NTFS is, GPT is just a method of block allocation once the filesystem is chosen, just like MBR. You can have an MBR disk in NTFS (like I do) and GPT disks in NTFS. GPT was created to aid in the detection and use of disks greater than 2TB. UEFI is actually a BIOS type, the Universal Extensible Framework Interface was created by Intel to allow more security options for newer systems.

In my 12 years or so of experience when a drive is unreadable, slow, or prompts for a format, that usually means that the drive is corrupt or broken.

I have a 1TB Seagate drive that failed (PCB), can't hold data past a couple of reboots. Another laptop drive gets stuck in repair mode through Windows 8 because it's physically damaged.

So either the drive is broken or the SATA interface on the motherboard is damaged. I had an Optiplex 3010 where only two of the SATA ports worked.

You assume incorrectly that windows can mount a newer os as though the drive was mbr and you are using msdos.

This is not the case.  It would be the same issue if you had msdos 6.22 and the drive was formatted FAT32 from WIN95C or WIN98SE it would see an unformatted drive.

If you use an apricorn USB drive wire or any other USB Drive wire the system WILL MOUNT the drive when you have WINDOWS 10 boot drive or Linux like UBUNTU 12.04.5 or higher or MAC OS that understands GPT UEFI and Secure Boot.   The only way you would see the drive under 7 is if it was formatted EXFAT.   You cannot boot from that.

The drive is not partitioned MBR it doesnt have a FAT or EXFAT Boot sector.  It has Hidden UEFI and MSR and then the Rest of the GPT NTFS Partition.

Secure boot was designed that way.  Windows 8 or 8.1 os will also NOT SEE a Windows 10 Secure Boot formatted Drive.   You can in fact format Drives SECURE BOOT OFF LEGACY CSM ON that are 2TB or smaller with MBR and NTFS and they will boot and be seen by other OS.  GPT is required for any Drive larger than 2TB.

So you could also attach a macbook with OSX and Read the drive.   Only RECENT Versions of Apricorn software work correctly with Windows 8 and even newer ones are required for Windows 10.

OP, if you're having trouble recovering files, don't use Apricorn. Just create a bootable Ubuntu flash drive, it has almost all of the software required to read most filesystems. The live install disks come with something called GParted, and as long as that's installed in the live OS you'll have all the libraries needed to read foreign filesystems. You can boot natively via USB on the customer's system or pull the disk and use some sort of other host. Once inside Ubuntu you can read and write to mounted disks, and you can even plug in external drives to back up data from. If you work in repair (as inferred from "I have a customer") then you should be familiar with Linux unless you're uncertified.

WINDOWS 10 will see a Windows 10 GPT drive but windows 7 and 8 will not.  DOS and WIN9X worked in the EXACT same way.  MBR is a partition Type As is EXFAT.  The Security parameters do not allow mounting the file system.  Linux and MacOS will mount the file system but in a READ ONLY state.  The other issue could be physical damage which may show folders but wont EVER be accessable.

With a Windows 10 boot drive there will be an error when browsing the drive.

Error: "You don't have permission to access this folder. Click continue to permanently get access to this folder"
When you click continue another dialog box comes up saying "You have been denied permission to access this folder.  To gain access to this folder you will need to use the security tab."  I click on the security tab link and another dialog box pops up asking "To continue, you must be an administrative user with permission to view this object's security properties.  Do you want to continue?"  

You may also have to take ownership.

- Right Click on the  hard drive and right-click the root of the drive.
- Click Properties.
- Click the Security tab
- Then click Advanced
- You'll see a window with some usernames. Now click Owner in the tabs above.
- Click Edit, then select the username you wish to be able to open the folder and be sure to check
the box that says "Replace owner on subcontainers and objects" then hit Apply.

A pop up will come up that says 'You have replaced the ownership for the selected folders'

In order to use or read a GPT disc, you need to be running the latest version of Windows 7 64-bit and the PC must have a UEFI-enabled BIOS.

That's not up for debate, as not only is this stated by Microsoft, but I had one of the earliest UEFI motherboards and I had a helluva time getting a GPT drive formatted and recognized as the primary boot drive. Once I had it setup as GPT, if I changed the BIOS setting to Legacy or moved it to an older Win 7 system (without UEFI), it would become totally invisible to the system.

Been there, done that, and the best way to alleviate any concerns with GPT is to just link it to a Win 10 system.