Hard reset or 30/30/30
From DD-WRT Wiki
Hard Reset or 30/30/30 reset
- press and hold reset button on back of unit...hold 30 seconds with power on
- unplug the unit still holding the reset button and wait 30 seconds
- plug the unit back in STILL holding the reset button a final 30 seconds.
This will clear out the NVRAM and set the dd-wrt back to default values.
This procedure should be done BEFORE and AFTER every firmware upgrade/downgrade
Do not use configuration restore if you change firmware builds (different svn build numbers)