I do not know why your menu option 3 did not work. Is your serial cable putting out the correct voltage levels on its TxD line? Is it rated as a 1.8v cable? If not, the kindle could be receiving the wrong character codes. You might need to shift the voltage levels, which can be done with a resistor and two silicon diodes (refer to the "level shifter" thread).
You erased device mmc0, which contains all partitions, including main@mmcblk0p1, diag@mmcblk0p2, /var/local@mmcblk0p3, and /mnt/us@mmcblk0p4.
Luckily, uboot is usually stored in a small i2c or spi memory device on embedded systems like this, and it is responsible for mounting and mapping an mmc device into memory (as either a block device or an xip* device), and then continuing the boot process from mmc. You should be able to boot to that uboot menu and try option 3 again after your serial adpater TxD is putting out the correct 1.8v ttl voltage levels.
If you have mmcblk0p1 backup up, you should be able to restore it so you can boot up main. Booting main will automatically format and populate the /var/local and /mnt/us partitions. From main, you can restore mmcblk0p2 (after jailbreak and usbnet).
If you are missing backups, you can use somebody elses, but you will need to use diagnostic tools to change the serial number and board ID to match what yours needs to register with amazon.
*xip = execute-in-place (not used by kindles).
Last edited by geekmaster; 01-10-2012 at 04:58 PM.