Blank Screen on Upgrade

Hey, all,

I’ve tried upgrading to 2.9.1 for a while now, and every single time, I get a blank screen after the upgrade process. The site runs fine, but I can’t get into the backend anymore. It’s like being stuck in a constant upgrade loop:
http://theportablegamer.com/wp-admin/upgrade.php?step=1&backto=/wp-admin/index.php

That just gives me the blank page. This is a new theme, so that’s not the issue. Anyone dealt with this before?