Raspberry Pi Wont Boot After rpi-update (Kernel Update) - Solution
When you update your Raspberry Pi running Raspbian [with rpi-update] there is always a chance your pi wont boot. Either you get errors or you get a blank screen and the motherboard only has the red light.
If your SD card is not corrupt its possible that the kernel is buggy and will not boot.
Luckily you usually have a backup. Look in your root /. There should be a /boot.bak folder.
So take the SD card out and put it in another linux machine. It may automatically mount. I'm going to assume you know how to mount the SD card.
You'll have two partitions. /dev/sdb1 is a vfat windows partition. /dev/sdb2 is a linux partition.
Go into partition 2 and go into boot.bak. Copy everything.
Go into partition 1 and paste everything (overwriting all files).
Issue "sync" command. Issue "eject /dev/sdb".
Recorded 1/1/2014