Cant access my Dashboard

Hi guys,

I have installed a theme called Arche and been using it for sometime now. But recently a worrying phenomenon arose: I could access the login page but couldnt access my dashboard. The Site and everything else runs just fine though. I managed to restore the site to an earlier backup but aftera successful login, the next time I coudnt access my dashboard.

Site: fhgkenya.com

Someone help a brother ??