Revive a dead phone? I don't have any background information, but my coworker showed up today with a nonresponsive Samsung Galaxy Gio. It will not boot. When plugged into the power charger, a half-full battery displays and just stays there.

Attempting to turn it on while holding the home button has no effect.

I swapped batteries with her (this is a company phone; we all have the same model). My phone works fine with her battery, hers does not work with my battery. Tried gently brushing off the battery contacts in her phone, no go.

Anything else to try before sending to the manufacturer?
It could be that the phone is stuck in a boot loop at or before the OS has a chance to load. According to XDA, to get into the recovery partition, start with this: Home button + Volume button - + On button.

If you can get into fastboot mode, you can issue a command from the PC with a usb cable. After seeing if the device is there with "fastboot devices", try "fastboot erase cache" and try to boot. If that fails, "fastboot -w" will essentially do a factory data reset. Of course, your coworker will lose all her data, but at least the phone might boot.