I’m on Media Temple as well. However, I do have other EE installs hosted there that are having no issues.
The password reset function work fine but the new password did not allow me to log in. Changing admin to sessions only in the config (and clearing the browser cache/cookies) had no affect.
At one point this afternoon when I changed debug from 0 to 1 in Admin.php it allowed me to log in and see the dashboard but immediately knocked me back to the login screen as soon as a clicked a tab.
I have tested in Firefox, Safari and Chrome. My client has tested in IE and Firefox with the same result.
In Safari it actually appears to log in momentarily and hang then goes back to the login screen.
My entire site is not down. I do have a section of the site that has extended functionality for members once logged in. (Not through the control panel.) Login on that side of things doesn’t work either.
Keep in mind that this site has been launched and working perfectly for a month and we have made no changes. This issue occurred out of the blue this morning.