[Galaxy S I9000 Q&A, Help & Troubleshooting] adslee:
Sounds like you've got the boot-loop problem, which means that you most likely "soft-bricked" the phone. Don't worry, this isn't that big of a deal and can be fixed with relative ease. I agree with the posters above, a clean flash with Odin will probably fix your problem and get you out of the boot-loop.

I'll go into a bit more detail with some steps (feel free to correct me if I missed anything)

1. Download Odin 1.85 here.

2. Head over to Samfirmware.com and grab the latest firmware for the phone. I recommend Gingerbread 2.3.5 (JVT).

3. Make sure your computer has the proper drivers installed so it can communicate with your Samsung Galaxy GT-I9000. If you've flashed the phone before with your computer then you probably have the drivers installed, but here's a link for them just in case: Samsung USB Drivers

4. Enter download mode on your phone, depending on your firmware, it could be Vol down + power + home OR Vol up + power + home. Pull the battery out, pop it back in, and hold those three buttons until the phone turns on.

If you can't enter download mode with the 3-button hold method, then you might have to do so via ADB with the command "reboot download".

Getting into download mode is pretty critical, as you cannot progress further without it.

5. Once you're in download mode (should see a triangle with an Android shoveling stuff in it), plug your phone into your computer's USB port and open Odin. In Odin, press "Reset" on the right hand side. Odin should be able to detect your phone (this is indicated by a yellow box on the left side). I'm using a PC, so inside the yellow box I see something like this: 0:[COM9]. On a Mac it probably says something different, but as long as you see the yellow box appear then it's all good.

If you don't see the yellow box, then there's no communication between your phone and the computer, which means that you may have to reinstall the Samsung USB drivers.

6. With the contents in the firmware package that you downloaded from Samfirmware.com extracted, load them onto Odin accordingly.

PIT: use s1_odin_20100512.pit

PDA: JVT (sometimes the PDA is labeled CODE instead)

PHONE: JVT (sometimes labeled as MODEM instead)

CSC: use HOME-MULTI-OXAJVT (should be about 9.5 MB in size)

Since your father-in-law's phone was originally 2.3.3, you shouldn't have to alter the bootloader with Odin, so leave the bootloader field empty.

7. Once you've loaded up all the necessary files, make sure Re-partition and Auto-reboot is checked. Leave the rest of the checkboxes as it.

8. Press Start. This should initialize the flashing of the new firmware. After the phone has been flashed, it should reboot automatically and should hopefully be able to get past the Galaxy S black and white logo (aka. boot loop).

9. The phone should be in working order now. I used this method to unlock my SGS: SIM Unlock on the SGS. With this method, your phone needs to be rooted, so head on over to ChainFire's thread here to install his kernal which is already rooted.

Flashing firmware can be pretty scary since nobody wants to end up with a brick that costed $400 and it seems like so much can go wrong, but hopefully the steps I've provided helped. Good luck!