is your new xbox a 1.6 or 1.0-1.5 and your bios is not compatable?.
or if you were using a bios that is compatable with that xbox, is the new xbox a 1.6 and needs a lpc rebuild?
"have you tried other banks on the chip?"
kind of struggeling here as you dont say what bios you had, what the previous xbox version was or what the new xbox version is..
any way if its something like you had a 1.0-1.5 and now you have a 1.6 the lpc is rebuilt but the bios isnt compatable and you have tried all the banks.
and you do need to flash it.
the xbit should be able to connect to your pc though, and from there you can select which bank to flash if you use the tool for it.
you would use the right sized bios for the bank you selected..
256k.. 512k.. 1mb.. and so on..
apart from that and the advice to recheck all your solder work, or if its a pogo thing make sure its seated right. Cant really help.