Although I dont like to recommend this, I think it's probably best:
Open Run... again, and type the following:
dcpromo
This will guide you through the uninstallation of AD. After it is done uninstalling, type dcpromo in the Run... window again to reinstall AD.
Make sure that you select the option to have AD automatically set up DNS for you.
I think that this problem is stemming from some weird DNS problem that would be really hard for me to fix without actually being there.
Sorry I couldnt give more concise advice, but like I say, it's kinda hard without actually being there.
