Tried last night to upgrade my system from FC2 to FC5. All seemed to go 100% until the reboot. The (boot loader, I presume) screen comes up which asks you to press enter or something to choose your system (only one option in my case: fc5) and after that I get

Kernel panic - not syncing: Attempted to kill init!

What on earth does that mean? Where do I even start to figure out what is wrong here?