Hello Mary,
Welcome to Microsoft Community.
As far as I know, when the general login system appears "security log is full“ this prompt, most of the use is the domain account (you mentioned" my admin ", but the personal device usually only one person to use, and should be the administrator). Could you please tell me whether this device is a company device or an organization device, and whether you are using a personal account or an organization account?
If this is an organizational device, then you should contact your IT staff directly to deal with the problem, perhaps they can solve the problem.
If anything is unclear, please do not hesitate to let me know.
Best regards,
Mitchell - | Microsoft community support expert from MSFT