I would copy all the skins from /Data/skins into /Data/Sites/[SiteID]/skins
then go into the database or have David Neal do it if he is willing and set the skin to one of the provided skins in the mp_Sites table, then touch your web.config file. That should get your site working again then you need to figure out what you have wrong in the skin that you do want to use.
Hope it helps,
Joe