If you have a Thompson drive in your xbox, good luck.. it's a pain in the ass
Those drives are picky about what brand/type of media it will read.
#1, Don't use CDR's
#2, Thompsons like Verbatm CDRW's
#3, Try a DVD-R if you have access to it
I messed with my first box for 10 hours.. I finally burnt the slayers install on a DVD, and even then, I would have to reset my box 10-15 times just to get it to read the slayers image just once... My advice, once you get a dash to load, FTP into your box and transfer your files that way (but first make a backup of your C and E and it's also a good idea to use a program called configmagic to make a backup of your eeprom)