Hi,
If there is some major error making the site unavailable surely there is an entry in the Application log on the machine.
I would download the mojoPortal log from /Data/currentlog.config if it exists and check the errors at the bottom of the file for clues. There will likely be a lot of errors at the top from initial installation, there are aways a series of errors because the tables don't exist until after setup runs.
The only kind of thing that comes to mind is if your host moved things around or changed file/folder permissions, like if the web process has no read access on the folders it could result in this kind of failure.
Only other thing I might do is purge all rows from the mp_TaskQueue and mp_IdexingQueue tables, then recycle the app pool, in case there are and tasks that got corrupted data.
Hope it helps,
Joe