Iphone 3g complete crash!

hello ginko i wondering if you could help me. i have an intel imac and an iphone 3g  which 'was' jailbroken. when i was playing on an app 'downloaded from the jailbreak software (cydia was what i downloaded it from)'. the screen went blank and the spinning icon appeared. a few minutes later the apple logo appeared. i waited a while, 'maybe about 20-30 mins'... and then i held the home and power button reseting the phone. still the apple logo stayed on the screen even after 20 mins. so i put it into DFU mode and of course itunes loaded up on my computer as expected. so i thought screw jailbreaking it coz its already messed up my phone so much. i just want to restore it to what it was like when i first got it. (obviously i would load the apps i downloaded from the apps store later on and my music and such) but when i click restore it says....the iphone "iphone" could not be restored. An unknown error occurred (2006).    ...   i'm so sorry my story has gone on for so long but any help will be greatly appreciated.