If you forgot your local user password on Surface Pro/RT running Windows 8.1 or 8, the useful way is to log into another admin account or use Previously-created password reset disk to change the password. However, these suggestions may be not working and the tablet does not recognize password. TO resolve the big problem, you could try those tips to do a full reset and recovery it. (Note: It will delete all your files.)
How to reset forgotted password on Surface Pro
By signing in your Surface 3 with PIN code or Picture password
* When the login screen shows login password is incorrect”, choose other sign-in options under user password input box, type four digital codes or draw three gestures on picture, and press Enter.
* Open the Command Prompt with Administrator, input the command:
net user your-user-name new-password
and press Enter to execute it.
If you have enabled the built-in administrator before, the Administrator account should be listing at the bottom side of login screen. Select it, login system without password, and make changes with your account.
Other way by doing a factory reset if you don’t care about file data loss
* First shut down the device and then press Power button to turn on.
* When Surface Logo with circling dots display on the screen, hold the Power button for 10 seconds and repeat it since you see the words “Preparing Automatic Repair”.
* In Recovery Mode, tap “Skip this drive” with Bitlocker, and go to Advanced Options > Troubleshoot > Reset > Just remove my files. You need to wait for about 20 minutes.