Hey. I JUST had this problem happen to me, not really sure what caused it.
I can't give much background, sadly, because I haven't been following xbox mods for sometime. I was a heavy follower of the scene about five years ago when I first did my box with a xenium chip.
edit** just saw my sig didn't realize it had stats in it. The modchip type is probably correct but I am not sure if I changed the BIOS since then. Also I don't run avalaunch dash anymore, just XBMC.
I have a test tomorrow so I was gonna watch a movie before bed. I put my DVD into my computer DVD drive and turned on my xbox. I usually stream my movies over the network from my PC because I don't like using the Xbox drive to read cds. I believe it scratched some of mine way back in the day before I added a harddrive, I also don't like adding extra wear to the laser which isn't necessary.
I went to play the movie from my DVD share and it never loaded and appeared to be hung so I turned off my xbox. I turned it back on and got the xenium safemode screen. I had no clue what it was, hadn't ever seen it before, and it said a message it loaded something from the HD. I was confused but it didn't seem to be doing anything so I powered it off. I tried to power it on again and got no response from AV cables. The modchip light was on normal, green LED on front of xbox was on like normal. I was extremely confused since I never encountered anything like this... I would have expected fragging...
I found this thread right away, lucky me, that mentioned the switch on the modchip (I didn't even remember it having). I haven't opened my xbox up for at least 2 years+ now and it did feel really good to get my hands back inside an xbox again
I flipped to safe mode, turned on xbox, got the safemode screen saying it recovered from HD (same random screen I saw earlier)--I decided to wait a while longer this time since I was expecting it....then it shut down on its own (I probably flipped it off a few seconds before when I ran into the problem earlier). I flipped switch back to normal position on the chip, turned on the xbox and all looks well again.
The hardest problem I had was trying to get the case back on the top of xbox believe it or not.
I am not really sure what caused this problem. It seems like the BIOS on the chip got corrupted somehow but I didn't do anything that would have done flashing towards the chip, just running standard software. Eitherway, I am glad the chip was able to recover itself. Would have sucked if I had to buy a new chip and relearn how to do a new installation or spend days looking into information when the fix only took about 10 minutes
I love this forum, it is still extremely helpful after all these years....