Ubuntu 8.04 Alpha6 booting into busybox CLI

What should one do when booting Ubuntu gets the Busybox CLI screen?

I just installed Hardy alpha6 on my Dell Inspiron E1505 / 6400 laptop (2 gHz Intel DuoCore2, 2 GB RAM, ATI X1400 graphics). I can get through the Hardy installation just fine, but upon first boot I get the boxybox cli. I tried adding the parameter "ircpoll" to the kernel line in grub, but this did not help. I have also tried various noacpi parameters and some vga=* parameters. When I remove the "quiet" kernel parameter from grub, I see that the system mounts the root filesystem, and then is waiting for the root filesystem. It never stops waiting, until it goes to busybox. In busybox I can browse the root filesystem.

What can I do to diagnose the fault? All I've been able to find in Google were suggestions to start disconnecting hardware: something that I cannot do on this laptop! Thanks in advance.

It seems that reinstalling from the Alternative Install disk (not LiveCD) leaves the system in a bootable state. So the problem has a workaround, however, I'd still like to know what to do in the future. Thanks.