May be it is a hardware issue i had a friend who had a similer problem got it fixed for about 15 euros
take it to some store see what they say
Best of luck buddy !!
hey! thanks a lot for the answer! look, i'v been to some shops and they all asked me for like 80 euros. I even tried playing dumb at the apple store and they asked 150 euros for a replacement + the iphone. ahm...but i'm not that dumb, considering that with a maximum of 200 euros you can buy a mint condition 32gb 3gs. So i sold it, took 30 euros out of my pocket and got a good 16gb 3gs.
Still, if anyone has a solution to this issue, i'm still curious about it...