hang on isolinux....

[Selenia]

I have found device identifiers a bit flaky on some computers, even more so when some usb drives are thrown into the mix. I had 1 such box and had seen a few others. Best policy IMHO is to always use UUID to mount, including in GRUB and fstab. Only time I seen a UUID change is after a partition is formatted. May I suggest SystemrescueCD, which is not only a great utility to do your Gentoo install, but gives you other basic Linux tools to help repair and troubleshoot. I would personally use fdisk -l or use the built-in GParted to see what is mounted where. Then do blkid <device path> to identify the UUID. There is a small chance your live CD, even SystemrecueCD, will mount things with a slightly different enough timing that the device paths will be different from your installation. However, the UUIDs will not change. Sometimes, you may find different device paths each time you boot from weird BIOS behavior as some OEMs may not follow standards correctly or some devices may take extra long to initialize. UUID prevents these potential race conditions.

Note that even if you use UUID, you best make sure the grub MBR install is installing to the right disk, which fdisk -l will help with. If this does not work, you may have to install it to a root partition(instead of MBR), though I have yet to have a case that requires that