how to fix a "bricked" iphone 3g,

Only hold home and plug in the iPhone.
If need be hold sleep and home for 10 seconds, then only home.
The iPhone will show on iTunes as DFU Recovery Mode.
Afterwards restore as a backup/new iPhone.

If that doesn't work, the genius bar is your next stop.

Try to put it in DFU mode:

1. connect iPhone to your PC (open itunes)
2. press power and home bottom same time appx. 5 sec.
3. when the iPhone restart release the power switch, but keep home bottom pressed
4. when iTunes find the phone and offer to restore it, follow the instructions