Hate to ask can you write out a step by step outline of what it was that you did to get it working?
You have to have a USB Mod to get it to work. I'm using the one that aliak11 made for me.
1. Plug it in to sd card slot or adapter on your computer and turn it on. The 3DS screen may stay black or have a blue error screen. This is normal.
2. When it's recognized by the computer, it'll ask if you want to format. DON'T DON'T DON'T DON'T do this. Just cancel.
3. Download win32diskimager, point it to the 3ds device drive, then click read. This will dump your onboard nand. It'd be a very good idea to dump more than one and check the hash info to make sure they're the same, so that you got an accurate dump. EDIT: Safely remove your 3ds and turn off before your remove your onboard SD card and plug it it, we'll be playing with its EMUnand partition now.
4. Use emunand tool to extract the emunand.bin from your emunand partition into a readable file. Again, do more than one and check your hashes. EDIT: When you're done, safely remove your SD card, put it back into your 3DS. Then plug your 3ds back into your computer MAKE SURE TO HIT CANCEL ON THE WINDOWS FORMAT PROMPT.
5. We'll take this emunand.bin into win32diskimager, then click write to write back to the 3DS. After doing this, right click that drive to safely eject. Then hold down the power on your 3ds, and the blue light will eventually turn off.
6. When you reboot, you should be on 7.1 or whatever the emunand was on your onboard. Go ahead and update to 7.2 and get whatever you want back.
7. After your done, turn off the 3DS. Plug it back into the computer and turn on MAKE SURE NOT TO HIT FORMAT ON THE PROMPT AGAIN.
8. Win32diskimager, click read to dump your 7.2 nand. Then write back your 4.5 nand to the onboard nand. EDIT: Safely remove your 3DS, turn it off, then plug in the onboard SD card into your computer.
9. Use the emunand tool to import your 7.2 nand into the emunand partition.
10. EDIT: Safely remove your SD card, put it in your 3ds. Withe verything done, it should be back on 4.5. And when you load gateway, you'll have a 7.2 emunand with your patches or whatever you got on it. Enjoy.