Hello, I’m Virginia an independent advisor with 20 years of expertise in fixing my own & friends’ PC problems.
Which Windows version are you running - 1809, 1903 or 1909?
Was the drive connected to a Mac computer previously?
It may be a case that the drive’s file format isn’t PC compatible so would require formatting to be able to be read, however this would mean losing all the files so isn’t an option yet.
Does the drive have a letter assigned? If not the do this via drive management.
Do you still have to old laptop? Is it Windows or Mac? If Windows then you can copy all the files from the drive to the laptop, then plug the drive in to the new Dell & clean it via diskpart:
Open powershell with admin & enter:
Diskpart
List disk
Select disk X (where X is the drive number shown under list disk)
Clean
Now you can close Powershell.
Go to disk management & it will ask you to initialise the drive - allow this, not you can format the drive & it should be viewable.
Now you can connect it to the old PC & transfer all your files back to the drive.