Accessing data on file shares happens with the user account you have created and use also on your local PC. Since this works, your network seems to be intact. Is the connector icon still up and showing its screen if you launch a console session from it?
Administrative tasks are only controlled by local Administrator account, which uses the console password.
There are some tools, which allow to reset the Administrator password if you can boot the machine from a floppy disk or USB stick, which should work also for WHS. Since this depends from the hardware (a blind flight is hardly possible with those tools and
without video card), you may have to perform the server reinstall process. This reinstalls the operating system, deletes all users and customizations, but keeps your data intact. (Anyway a backup of the data stored on the server to some different, disconnected
media is always a good idea.)
Best greetings from Germany
Olaf