I've had a similar issue with my own DIR-825 Firmware version 1.11NA, hardware version A1.
Router stops WAN forwarding, but continues LAN forwarding (I can remotely access a networked computer on my LAN) and refuses to acknowledge admin page access. This happens after less than 24 hours of use.
I have since temporarily replaced it with a Linksys WRT610N that I happen to have lying about. I eagerly await a revised firmware for the DIR-825.
There have been multiple releases of v1.11 with different file dates, but the binary of each possess the same MD5, but with differences in the text file containing the changelog. -- HCN: Because you deserve a rest!