You can corrupt the hack by turning on the Xbox without the A/V cable plugged in, and then plugging the cable in (which will then boot the Xbox).
To fix it, replace the ST.DB file.
If you're using the old swapless audio hack (the one that loads E:\linux.xbe), then you can corrupt it by copying the blank soundtrack over itself (instead of copying it to a new soundtrack).
To get rid of this problem, get the stable swapless audio hack (see 4th post).