I was monkeying around with my X-Chip and hosed the bios today. I looked everywhere, but couldn't find a fix. In a nutshell, I could see the bios via the USB X-Control software, flash the bios, read and write it, but the X-Box (v1) wouldn't boot. I knew it wasn't hardware because it happened the moment I put a new cromwell on the chip. Of course, I didn't back up my raw, so I was hosed. And even though I knew that it wasn't hardware, I did the due diligence and pulled the chip and was able to boot to the stock XBox dash.
I spent hours looking for a fix for this. I tried multiple different Bioses in different spots on the chip. I was getting pretty damn frustrated when I discovered that in the x-chip install folder, there's a bios file (C:\Program Files\X-Chip\BIOS) to overwrite the whole thing. I figured, what the heck, backed up my hosed chip and flashed it with the file I found. I then put the same x2_4983.67_256k bios in the same slot it had been in previously, set it to boot, and wrote it to the X-Chip.
It worked like a champ.
So what I got from this was:
-People have moved on from modding xboxes, or at least, it's not a mainstream thing and the actual experts are doing new things so you won't be able to get much help.
-Never mess with a working, modded xbox.
-Always back everything up.
I hope this helps some people out there who have had similar problems.