I cannot enable sa account

You'll have to use sqlcmd.exe with Windows Authentication (Specify the -E flag) and renable the account:

Open up command prompt and navigate to the SQL Directory and use sqlcmd.exe -S server -E

USE [YourDatabase]
GO

ALTER LOGIN [sa] ENABLE
GO

http://msdn.microsoft.com/en-us/library/ms162773.aspx

1. Launch SQL Server Configuration Manager (as local machine Administrator)
2. Select SQL Server Services -> SQL Server Service on the right side
3. Right-Click on it -> Properties -> Advanced Tab
4. Into "Startup Parameters" string add ';-m' to the end of string -> This will bring SQL server to 'single user mode' in which local machine Admins have super-user rights.
5. Restart service in order Startup Parameters to take effect.
6. Login via SQL Server Management Studio using Windows Authentication as local machine Administrator -> now it has super-user preferences and allows you to change everything.

login with windows authentication and select server properties and go to security tab check the bubble SQL server and windows authentication click ok.

or

run below query

ALTER LOGIN [sa] WITH PASSWORD='AnyStronG@#Passw)e', CHECK_POLICY=OFF
GO
ALTER LOGIN [sa] ENABLE
GO

Ref:- Enable Sa Login