If you have not done this already.
In whichever browser delete the panel.dreamhost.com cookie and any other dreamhost.com cookie.
Empty your browser cache. Close the browser and now try and see if that works.
If you still have no success then repeat but this time reboot your computer to make sure there is nothing left in memory. Try again and cross all digits.
Sometimes the panel can take a while to load. Sometimes a few minutes. (Not very often MikeS .)
Opinions are my own views, not DreamHosts'.
I am NOT a DreamHost employee OK!! :@
You act on my advice at your own risk!