Problem installing wp theme and upfront

Hi. Need help. Have big problems with our customersite. At first the page did respond very slow. Then we were unable to update anything. To make a long story short - we erased all files, even WP. Then we installed all files (fresh ones) and off course a new wpmudev dashboard. But.... still the same problem, we can not install themes, upfront and update takes the world in time. No help from webhotel owner one.com. Have you any clue? If anyone wants a login, please tell me. I am in need for serious help here.