The Linksys WRT54G is a great little WiFi (Wireless-G) home router, and there are a number of communities out there that  have created custom firmware to run on them. But one of the risks of flashing your router with new and different firmware is that you might just end up with a useless brick, typically characterized by red flashing lights and a severe lack of functionality.

If you can't get a SFTP upload of the default Linksys firmware to apply to the router using their utility, it's possibly toast. But there are still a few options (try at your own risk).

First of all, though: Have you tried to upload a fresh copy of the Linksys firmware using the Linksys utility you can download from their web site? Was your router running the Linksys firmware or one of the community firmware builds when the problem started? Depending on the firmware and router version, you might find that you need to go back to an older/original firmware file, then re-apply the custom one. Your mileage may vary, but if you're bricked you might not be worried about things like warranties. Just be aware of the fact once you start messing with stuff, warranties are often a thing of the past.

Here's a few links to try to help - feel free to leave a comment if you know of others:

• Red Diag or Power Light Blinking on the WRT54G:
  http://tinyurl.com/7al4s
• For the courageous:
  http://nino.net/blogs/nino/archive/2005/06/09/744.aspx
• More info on un-bricking it:
  http://www.barik.net/archive/2004/12/03/220751/