Unable to mount old internal

First up hello and thanks for answering a newbie's dumb questions. I appreciate it.

So my original 500gb Internal hard drive was having issues after my gf dropped my macbook pro. It worked but slowly and the hard drive was making noises spinning. I removed what data I could but it was laboriously slow. Worried it would collapse and I may lose data using it as was and basically unable to perform most tasks well, I have since removed the internal drive and connected a new SSD and everything runs fine and fast as before.

However I still have data on the drive I wanted to fetch at a later date. When I load the old internal hard drive in a Nexstar Dock it says "The disk you inserted was not readable by this computer" and gives me the option of Initialise, Ignore and Eject. I select Ignore and it shows as available on the left hand side as "500.11 GB OEM Ext Hard Disk Media" but the "disk1s1" below is greyed out and I am unable to mount it. The following disk information is available:

Name : OEM Ext Hard Disk Media

Type : Disk

Partition Map Scheme : Master Boot Record

Disk Identifier : disk1

Media Name : OEM Ext Hard Disk Media

Media Type : Generic

Connection Bus : USB

USB Serial Number : 00000000000000E4

Device Tree : IODeviceTree:/PCI0@0/EHC1@1D,7

Writable : Yes

Ejectable : Yes

Location : External

Total Capacity : 500.11 GB (500,107,862,016 Bytes)

Disk Number : 1

Partition Number : 0

S.M.A.R.T. Status : Not Supported

Is my old internal hard drive unaccessible because of the way I removed it? Can I remove the SSD and reconnect the old internal hard drive and salvage what I can? Can I reconnect it and run a program like DiscWarrior. I am at a loss and there seems to be no information about accessing an old internal hard drive.

Please help.