If the built-in Administrator can't open the User Accounts control
panel, nobody can. You either messed up when you were "installing all
new software" or your computer is infected or there's more to the story
than we know.

In Safe Mode after logging on as the Administrator (note that there is
no "s" at the end of the word) open the Security permissions on
C:\Windows and try to give Authenticated Users full control on "This
folder, subfolders and files". Then 'OK' your way back to the desktop
and try again to open the User Accounts control panel.
---
Leonard Grey
Errare humanum est

MRD wrote:
I did as you suggested but after signing in as the built-in administrator I
was not allowed to open the Users option in the control panel. Access was
denied. Anything more I can do? Thanks.