Some time ago Cydia crashed, in opening it kept returning to the SB. I tried to solve the problem with diskaid and with the terminal (apt-get...) but it did not work. In the end I restored my 3G 16Gb OS3.0 and did another jailbreak. At the moment Cydia and the apps I downloaded with it are working fine.
The problem now is that ALL the apps I downloaded from the store are not opening, they return tot the SB.