Just thought I'd mention this from what I've read so far: it sounds like whoever modded this Xbox might have cut a trace leading to the Xyclops chip, containing the original Xbox BIOS. Can you check the traces near this onboard IC? If this is the case, it is impossible to boot from the original onboard BIOS. You must use a modchip to use the console at all, or repair the trace. If the console cannot find a BIOS to boot from, it always tries three times then FRAGs.
I DO have a copy of the original MuppetX BIOS, I dumped it before reprogramming it manually when I first got it.
I can't attach it as it exceeds this forum's file size limit, so I'll post a link for anyone who wants it.
https://gargoyle.acns.pns.edu/xbox/MUPPETXBIOS.BIN
I also have a link to another forum (in foreign language) where someone described how to make a CD with the correct filename for overwriting the BIOS via the Xbox itself (with the modchip in) https://gueux-forum.net/index.php?/topic/193810-resoluflasher-sa-muppet-x/
I hope this helps! EDIT: I thought I'd mention, the MuppetX BIOS is simply a Cromwell-like loader used for reflashing whatever other BIOS you want to put on the modchip. It cannot by itself boot any Xbox programs. It's use was simply to avoid selling chips containing modified Microsoft copyrighted code, to leave the end user to find this for themselves.