My HP Pavilion 15 n-208tu Notebook(Windows 8.1)is not accepting password of administrator account

Hello All

   I have just bought a new HP Pavilion 15 n-208tu laptop(Product Number:F6C93PA) with windows 8.1 preinstalled.After successfull registring and creating administration account  i used it with no problem for few days .

  But now when i open it ,entering Administration Password it is showing error:The Password is incorrect.Try Again..

i carefull enter my correct password many times even after restarting ... on next day....but no solution Same Error

Please any one with solution to this,help me.

i will be greatly thankfull for your suggestions.

Ravi Patel