I would recommend you to follow the methods below to resolve the issue:
Method 1:
Enable Built Admin account.
a) Press Windows and x key together on your desktop screen.
b) Click on Command Prompt (admin).
c) Type: net user administrator /active: yes
Note: Please follow the same steps and type net user administrator /active: no to disable admin account after the troubleshooting is done
After enabling Built-in admin, please try with the steps below:
Step 1:
Perform SFC Scan
Please follow the steps to perform SFC Scan:
a. Press "Windows Key + Q" to open Charms Bar.
b. Type "cmd" without quotes in the search box.
c. On the left pane, right click on the "cmd" option and select "Run as Administrator".
d. Type ‘sfc /scannow’ without quotes and hit enter.
Note: It may ask for windows installation DVD to fix and to enable SFC to make more than minor repairs. Some files saved on your computer might get deleted when fixing corrupted files.
Please restart your PC and check if you are able to log in to your Default Profile.
Method 2:
From Built in administrator account create a new user account and transfer the profile data.
Please follow the steps below to do that:
a) Press Windows and x together and select Windows Explorer.
b) Click on View tab and Click on Options at the top right corner.
c) Click the View tab, and then click Show hidden files, folders, and drives.
d) Uncheck the box which states **Hide protected operating system files.**e) Click Yes to confirm, and then click OK.
f) Locate the C:\Users\Old_Username folder, where C is the drive that Windows is installed on, and Old Username is the name of the profile you want to copy files from.
g) Select all of the files and folders in this folder, except the following files:
•Ntuser.dat•Ntuser.dat.log•Ntuser.ini
h) Right click and Select Copy.
i) Locate the C:\Users\New_Username folder, where C is the drive that Windows is installed on, and New Username is the name of the new user profile you created.
j) Right click inside the folder and select Paste.
k) Restart your PC and check if you are able to log in to default profile.