can somebody help me please, i think i screwed up

its just that every time i start my xbox the error 21 shows up telling me to call customer support, the reason is this, i have a soft modded xbox and i set it up accidentally to do an autoupdate when xbox xtarts but i dont have xbox live or internet connection, so the error always shows up, i dont mind chnging my dashboard or formatting my drive but i just dont know how.

i was also told i could create boot disk, i have a evolutionx pack with bios files and different versions of the dashboard on my pc but i dont know how to use it or to create that boot disk

have you tried turning your xbox on with your dvd tray open, then pressing restore C backup?

That should do it.

Chris