I did that but Cydia crash as soon as I open it..I'v tried to delete the fils in /root/private/var/lib/apt/lists/ except for the partial subfolder, but don't have any files in there to delete, any idea?
I restore every time with Itune the 3.1.3 firmware (in this case) that I have downloaded from the net and than jailbreak with Redsnow, not sure what you mean with back up?
Not sure then why your cydia keeps crashing. If you want you can go to a 4.2.1 custom firmware with no baseband update in it. If you dont have access to a Mac just PM me and I can give you one.
cydia apparently crashs on all the older os's unless you use jailbreakme on an already activated phone, im on tmobile and for my 2g and 3g on 3.1.3 and 3.1.2 i had to redsnow to hactivate the phone then use jailbreakme right after to make cydia work. not sure if thats bad for the phone or not seeing as my 3gs updated and crashed atm on the ipad baseband... but my 2gs been like that since jailbreakme came out and it still working just fine.