I'm stuck after the instalation.

I completed the instaletion without any problems but when i try to run gentoo from my HD i get an error that /dev/sda3 isn't bootable. So i searched for some information how i can fix that.

Somebody said i had to do something with my genkernel.
genkernel --no-clean --no-mrproper --no-menuconfig --udev --install all

but when i start my linux with my cd and i type that i get an error message:
bash: genkernel: command not found

How can i fix this?

Or has anyone an guide to fix my problem completely?
I use x86-2.6.19-gentoo-r5