not giving up that easy....
heres something I thought of when re-reading your new post.
boot up slayers
select new install/full rebuild
select new install/full rebuild-retail HD
backup warning (got nothin to lose at this point)
select restore retail xbox hd to factory
select yes
(please note the drive will be formated and erased)
after ejecting the slayers disk, powering off the xbox, then back on you should have the m$ dash back. (maybe a newer/older one depending on your xbox version.)