Without running some diagnostics it is hard to say what the issue could be.
You can use this bootable Windows PE (Portable Editing) to run diagnostics. http://windowsmatters.com/category/windows-pes/
Worst case you can use the SSD for another computer be it the new one or another one.
Hmmm... Interesting. Had a browse through your replies above and didn't notice if anyone asked if your hard drive is actually seen by the BIOS. So in the section where your HDD's are listed do you see the hard drive listed.
Personally any time I'm fixing a computer with an issue I take a usb stick with Gandalf installed on it. http://windowsmatters.com/category/windows-pes/ it gives me all the tools I need to check the machine. And if the machine boots from the usb stick I pretty much know the drive has emotional issues.
Something with a windows 2000 install on it has a pretty old hard drive. 😁
Grab a copy of Gandolfs windows 10.
http://windowsmatters.com/category/windows-pes/
Install to USB
Boot
I believe (may have to look around) the path is programs > security > unlockers... But what you are looking for is ntpwedit.
Open it.
Choose the administrator account.
Right-click and unlock.
Right click and change password.
Do NOT enter a password. Leave it blank. SAVE changes.
Reboot and log onto admin account and undo changes.