How to change the iPhone 3 back to the original form? Or at least reset it?

My brother messed up the iPhone 3 and it can only do emergency calls. No apps, musics, videos, photos, nothing. Just emergency calls. My brother claims that he wanted to update some stuff, but he really means that he wanted to move the ringtones (musics, photos, apps, etc.) from his iPod to his iPhone. But he used the computer to do it, and sort of messed it up. Do you guys know how to change it back to its original form - the iPhone 3 - or a least reset it?

Added (1). Edit: My brother did in fact update the phone with the sim card. The sim card won't work. And I don't know where I could restore the phone.

Added (2). Edit 2: All right, I found how to restore it, but the thing is, something's wrong with the sim card. Anybody knows how to help?

Hold the power button and the home button for roughly 10 seconds then release the power button and keep holding home for 15 seconds then plug it into your computer and open iTunes it should have a pop up that says something like iPhone in recovery mode then just click restore.

Insert an att sim card in it.
if you don't have one, you can look up on youtube how to hacktivate iphone 3g 3.1.3
if that doesn't work, restore it with itunes and try the above again

From what I read your brother probably updated your iPhone to the latest version, which will require a SIM card from the original carrier where it was bought due to activate it.

There's nothing much to do than use an AT¨&T SIM card when activating or jailbreak it.