Windows Won't Boot after resizing partition

It sounds like the NTFS volume has been damaged. Before running gdisk, did you try to have Disk Utility repair the Bootcamp volume?

You need to try the Windows install DVD and run Windows startup repair. This thread, under "This solved my question" goes through what do to.

As you have learned you can not resize a Bootcamp partition using Disk Utility. The only way to resize a Bootcamp partition is to use CampTune. Now you will have to erase and format your hard drive. Reinstall OSx and Windows.

So here's what I think happened. Upon resizing the OS X volume, a 5th partition was created. When that happens, diskutil removes the hybrid MBR that's needed to activate the EFI firmware CSM (BIOS emulator) which is still presently used for booting Windows on Apple hardware. Upon removing the hybrid MBR, Windows is no longer bootable. So what you probably did was used Disk Utility to reverse what you did by deleting the extra partition. When you do this, diskutil recreates the hybrid MBR but with the wrong partition type code. It sets it to 0x0C, and therefore thinks it's FAT32, whereas it should be 0x07 for NTFS. Disk Utility will then let you run a disk check on what it erroneously thinks is a FAT32 volume, but is in fact NTFS. If any writes are done, which it appears is the case, it corrupts the NTFS file system.

So this is just yet another Bootcamp data loss story, without any warning in either documentation or Disk Utility whatsoever.

What version of OS X is this?

The easiest, but most tedious thing to do is to totally start over with everything: obliterate the entire drive with Disk Utility making 1 partition only, reinstalling OS X and files from backups, use Bootcamp Assistant to resize the OS X volume the way you really want it, reinstall Windows and restore from its backup. All of that can be done in the GUI.

You might still use the Windows install disk to run Windows startup repair. It might fix the Bootcamp volume. The remaining problem in that case is what to do with the large pile of free space, but I'll make those suggestions later once you get to that point.

If Windows startup repair can't fix the Bootcamp volume, and you don't have a backup, then you'll need to download and install testdisk, and read how to use it to try and find your data. It's an iterative process. Once that's done, while it probably won't fix it and make it bootable again, you'll have a basic backup of files. The remaining thing to do is use gdisk remove the broken Windows partition, make a new one that also includes free space you presumably wanted Windows to have, and make a new hybrid MBR adding partitions 2 3 4. Then reinstall Windows, your apps, and restore your data from backups.

So that's the gist. Ask if you have more questions.

The EFI was visible

I don't know what that means.

Bootcamp appeared as "disk0s4" after resize.

That's unfortnately expected (while being undocumented, is caused without prior warning, and Apple provides no tools to repair). So did you click on disk0s4 and try to repair it?

Strictly speaking a reinstall doesn't require a new version of Windows. It's just that Bootcamp Assistant blocks you from this. The old XP bootcamp.exe files/drivers are still floating around, so as long as you have older hardware that's successfully running XP, it's possible to reinstall it. Again, just not via Bootcamp Assistant. It can be done via Disk Utility or via command line.

EFI used to be one of the HDD symbols I would see upon initial startup while I held down the ALT key. I don't see this anymore.

That's not normal. With Lion + Windows you should see three options: Macintosh, Recovery HD, Windows.

You can see it but not be able to click on it. Interestingly it show format as MS-DOS(FAT).

Now? Or previously?

I'll try the Windows re-install and see what happens.

No, I suggested that you boot the installer and run Windows startup repair first. It's worth seeing if it can be fixed. And then next is testdisk if you don't have backups.

You really aren't paying attention. I explicitly said earlier you do NOT want to run Disk Utility on Windows NTFS volumes that Disk Utility incorrectly identifies as FAT32 because it will corrupt the file system if any writes are done.

6 hours ago I wrote:

Disk Utility will then let you run a disk check on what it erroneously thinks is a FAT32 volume, but is in fact NTFS. If any writes are done, which it appears is the case, it corrupts the NTFS file system.

Disk Utility != Windows startup repair. OS X cannot create or repair NTFS volumes. It can repair FAT32 volumes. Disk Utility is misidentifying the volume as FAT32 and attempting to repair it. You should not allow it to do this!

Windows XP is a long time ago, I'd see if you can even find a Vista or Windows 7 install DVD, with or without serial number. Use it manually as described in the bootrec documentation, rather than using the automated windows startup repair which probably won't work on an older version of Windows. But a newer chkdsk will. Use chkdsk first and see what results you get. Then try chkdsk \f to force repair without trusting the journal.

Even if you can't get it booting at least you can get data off of it. So it may still be worthwhile to go down the testdisk route.

Probably. But I'm unfamiliar with both that backup method, or the restore process. So either the exact steps of "how to restore" using that backup method needs to be specified, or the expectations of system state immediately prior to the restore needs to be specified. Then I can tell you what you need to do to your system to get it in that state, as it's pretty unlikely the GUI tools will help you do that correctly.