I have a problem with my board. Upgraded the firmware and the board does not boot again. Please help on how I can reload the firmware. Thank you.

Use netinstall and reinstall your router
http://wiki.mikrotik.com/wiki/Manual:Netinstall

thank you hozam for your reply, I have tried that but can't install as the install button is not active as shown in the screen shot. Please help on how to go about it. Thank you.