Unable to restore my iphone 3G

Hi guys!
Today I downloaded from itunes the last available software, but iphone didnt install it correctly and showed me an error according to which itunes suggested me to restore my iphone. Ok, I tried to, but while it makes the preparation to restore the phone, it shows unknown error (21) and aborts the operation! So, I dont know what to do - my phone only shows only an apple and nothing more!
Also I tried to restore it in DFU mode - neither it helps. I downloaded software apart, but when I try to chose it to restore, itunes doesnt allow me to chose a folder, neither the files inside it.
Do you have more ideas? I cant wait till monday for apple support shops to open ((((
MacBook Mac OS X (10.4.11)