It is a clear indication that either MDF or LDF files is missing.

Try below options:

• give permissions to the account running SQL Server service to the location where MDF & LDF files are located

• open SSMS with admin privileges

• modify the MDF and LDF files properties as below

right-click on the file in Windows Explorer, select Properties
select the Security tab
Click Advanced
Click Change Permission
Uncheck “Include inheritable permissions…”, a window will open
Click Remove (removes all permissions), the window will close
Click Add
Enter your login name and click OK, the permission window will open
Check Full Control – Allow
Click OK, OK, OK, OK