Ill Mitch, it takes some courage to stand up and say you did something wrong. Plus, it makes it look like it's not my fault that your Xbox is screwed up right now!
I'll tell you how to fix it, but before I do, I think it's better that you know more about your Xbox and what you did to it. What you did in Xboxhdm was format the C drive. You see, the Xbox hard drive is split into many different partitions. C is for any dash files, E is for all your music and game saves, and X, Y, and Z are all temporary cache drives which hold files for loading off the hard drive for later/quicker use.
You only formatted the C drive, meaning all of your Music and Saves should be fine (If I'm reading correctly). The Xbox is looking to the C drive to boot from, and since there are no files in the C drive at all, it is giving you error code 13, which is a dashboard error. But, you see, you can load Xbox games by coldbooting them. This is because the Xbox BIOS is set to look at the DVD drive for an XBE before the hard drive.
To fix it:
1. Download SlaYer's EvoX Autoinstaller v2.6_FINAL from the usual place. You will have to download a torrent, and then use bittorrent to download the ISO.
2. Download
Qwix. Use it to extract the SlaYer's ISO.
3. You will have to make a new XboxHDM CD just like the one you made before, but with one addition. You will copy all the files from your extracted SlaYer's retail full C drive.
/SYSTEM/ALL/C
Which should be the following:
AUDIO folder
FONTS folder
XBOXDASH folder
XODASH folder
xbox.xtf
xbox_book.xtf
xboxdash.xbe
4. Coldboot any retail Xbox game (Halo for example) and wait for about a minute. Load the new Xboxhdm CD you just made into your computer. Hotswap into the Xbox hard drive and type 1 at the main menu.
5. This time, type xboxhd like you did before and type 2 to restore C drive on existing xbox hard drive.
6. Then, turn off your computer after it is finished and the hard drive should work like a normal Xbox hard drive and it should boot up fine. Then, try the entire tutorial over again and don't make the same mistake twice.