Kenny and Joseph,
Turns out you were correct about our host. My sites are back up after much time spent on the phone with tech support. This is what they said:
It seems that someone configured the connection strings (in the web.config file) for SQLExpress instead of MS SQL.The only thing I worry about is the fact that the sites worked for four months before just crashing over night.If you guys have any other ideas about what went wrong, please let me know.Thank you,Jim