I upgraded my wireless router to one of the DD-WRT firmware, and after reboot the device did not come back. After many attempts find a way to rest, and here are the steps:
1. While holding in the reset button plug the router back in (this disturb booting sequence kind of like safe mode in Windows).
2. Now connect an ethernet cable to your computer (do not connect to the router yet) and configure it statically with 192.168.1.3 (255.255.255.9 as the subnet)
3. Now open a browser and go to 192.168.1.10.
4. Upload the factory default image.