You'll need to build an uImage for uboot, not a bzImage.
The led its on and not blinking? This means your kernel isn't loaded yet.
You could look here:
https://github.com/pazos/linux-2.6.35.3-kobo and see my commits for a working example for the Kobo Aura HD. The only thing missing from stock sources is the wifi driver.
ie: building the kernel you'll need `make uImage modules`