half working i phone is it a software fault

[jodie]

my boyfriend went and bought a 2g i phone on ebay but the sms messaging does not work space bar goes dead it is the saame on the internet u cant hit enter does nothing but it is fine on other apps it has cydia in itr how do i fix it if i can im hopeless with these things it is running version 2.1 if i take it back a version will it lock the phone again it seemingly happened when he updated from 1.4 anyhelp appreciated