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Why is it failing to load the stock bios when the mod chip is off
Its not to do with the stock bios not loading. the M$ bios is loading.
The problem is to do with the files on the HDDas mentioned by our friend HackDaBox.
If you want an easy fix for this use slayers to reformat and rebuild the HDD. make sure you chooese the correct options. all the original M$ dsah files and stuff will be replaced.
Otherwise its boot from the chip and FTP copies of the folders from a known good 1.6