Hi Balihai,
Have you changed your Betfair account, such as opening a new account? This would cause a problem needing you to reregister for a Cymatic activation code and reinstall the software.
Does it open a browser window which is blank, or just show you an empty Cymatic screen with no list of markets?
Was the login successful? Please check the Status Log tab to see if it says you have logged in successfully.
Which country are you trying to access it from?
Kind regards,
Gavin