How to unbrick a non responsive Gio
If you can't get the device to even turn on, then this will not really help...

From XDA post about unbricking this device:


Prepare ODIN with the firmware you want to flash (in my case was Gingerbread 2.3.4) and get it ready to go.
Remove battery, wait for a bit. Insert battery again.
Flash a recovery with your specific filesystem (EXT4 or RFS)-(If you have EXT4, download ext4 only, don't get ext4+rfs)
Enter recovery &amp; Wipe | Format:

System
Data
Cache
Dalvik Cache

Have ODIN ready. Connect phone to PC.
Reboot to Download Mode

Hold Volume down + Power + Home button at the same time.

At this point Odin should have detected your Galaxy Gio (Yellow rectangle should appear).
Insert the Stock Rom or Custom Rom.
Click Start button in Odin and wait about 5 min.
Reboot and wait 


The post has other options like using a tool called "one click unbrick" but I have never tried that tool.