requesting a password when restore

hi,

(since i have no other options)i have updated my i4 to 4.2.1 jb'd. now is it possible to restore to earlier v 4.0.

i am asking coz when i connected to itunes after jb it gives me an option to restore or setup as new iphone.

the phone is not carrier unlocked so if i could restore i can use it again. so i was wondering to restore and when i tried it requests for a password. i didnt use any password but used my lock code seeming that it was a password but it doesnt work.

thanks