iPhone fell and died

Here's what happened:
one day i came back to my house and plugged the iphone for recharge, it didnt start recharging so i thought the cable is dead.
after few minutes the battery was depleted.
at the same day my phone fell twice, noting too harsh tho.
next day i got new cable, and it seemed ok, it was charging but then i noticed the home button dosent work anymore.
ok i lived with that.
few days later the phone fell again and its dead since then.

its a 16GB 3g iphone. i bought it used for really cheap.
i decided to try and fix it myself because the prices are really high to fix this thing.
I thought its the bottom part of the phone cuz this is where the home button and the charging connector are located, so i ordered that part.
today i replaced it but nothing, phone still dead.
now im clueless and don't know what to do. any suggestions?
tnx

is it on version 3.1?

no, its 3.0
dose it really matters?

happy update:
I didn't gave up and tried to assemble the phone over and over and it worked, the phone is now working! its alive and the home button is working too!
lol, i was so frustrated and now im so happy haha.