Ok so heres the thing read the marriage theory posted by the one guy in the forums. Next Im gonna tell you that I have already had this problem before and i fixed my problem luckily.
If you still wanna use your same hdd and you dont want to buy another one then use xbox_clone.zip
pull out your old stock hdd make sure it can connect to live before doing so.
check your xyz codes on your modified box make sure they dont show any signs of being banned.
then just copy from your original 8 gb westerndigital hdd or any 8gb hdd that works onlive to your modified hdd using only xbox_clone.zip with the help of your computer.
you can find xbox_clone.zip in xbins under pc under hdd tools etc...
It has come to my attention that when you do that your copying a file from the c$ directory of another hdd that has your xboxs hdd and motherboard and eeprom information in it.
My theory is all they do is check there servers and then check your hdd with that file and see if everything matches up. If everything matches its good but if it shows that there has been a change with the hdd but not the eeprom then it will ban you.
Or partially ban your hdd. So by using xbox_clone.zip you can confuse the servers and make them think your running off of your old stock hdd.
thats the way my setup is I cloned from a western digital 8gb to western digital 80 then cloned to 200 and it still works on live havent tested halo 2 yet. It will be interesting.
Oh ya and i have no modified software on the c and e drives I have everything loading off of F: which the retail bios of a normal xbox cant see muhahahahahaha!