Plato Server and Clients
In the MDF are all the servers, including the plato web server, running IIS. In order to have Plato running all of the Plato Services must be running, as well as the Web Server in IIS. If you check these services and one or more of them is not running then restart it, and see if the server responds.
It might take some time to resolve an IIS problem, but if you right click the Default Server and make sure it is running and then go to the Services management MMC and check the Plato services , names like PWLN and so on, you ought to be able to spot the problem.
Reboot the server if all fails, but call Richard Hardt if you think this is over your head.