Dashboard gets 404 page for only one blog

Anyone ever see this before? I have over 700 blogs running, all work fine except one that cannot load the dashboard page. It sends to the front end with the 404 page. All other admin pages work fine even for this one broken blog.

Logging in through terminal and watching, every time I try to access the dashboard mysql goes crazy using 100% of the CPU for up to a minute, before I am guessing sending a 500 error that WordPress sends to the 404 page?

Currently using 3.0.5

Have tried the following...
switching themes.
disabling plugins
removed content from blogs.dir folder in case they were over their quota
reset permalinks

Any other ideas?