Is your Linksys WRT54G power light blinking continuously and not in working order? If it is, then it simply means you most likely have been playing around with 3rd party firmware and the previous firmware was not properly flashed.
Have you tried to re flash it but problems still persist? Then the following rescue method applies if your Linksys WRT54G still respond to pings at its default IP. As long as your Linksys WRT54G is a v4 or below, then you're in luck.
Basically you will be doing the same thing, which is to re flash the firmware but this time use this particular one which you can find here. Instead of a .bin file, you will flashing a .trx file.
If you have never flash before, then you can follow these simplified steps.
1. Download the firmware from the link above.
2. Set up your system (PC or notebook) with static IP of 192.168.1.2/255.255.255.0
3. Connect your system to one of the 4 ports on the wireless router.
4. Open up a command prompt and go to the folder where the firmware you downloaded from the link above is located
5. Power up the router
6. Execute this command and wait till it is finished
tftp -i 192.168.1.1 PUT openwrt-brcm-2.4-squashfs.trx
7. If the power light stops blinking, you've have successfully recovered your router!
You can access the router's management page through your web browser at http://192.168.1.1.
If you prefer to use back Linksys official firmware, just upgrade it through the web interface.