There are many reasons why it won't calculate. Have you tried using the calculate tax button icon to automatically calculate taxes? Have you entered your personal exemptions properly? Have you turned on the calculate tax box in the employee tax folder? Have you assigned a provincial tax table in the employee tax folder? Have you assigned pay periods for the employee in the income folder? Have you in the setup, settings, payroll, income tabs ticked off the income field to calculate tax?

Hope this helps!

thanks Brea .... 

It was the calculate tax box in the employee folder. Very odd as I haven't been doing anything different for last 2 years for payroll and suddenly it was not working.