I
suspect that the error message was that
chroot failed. That usually happens when GRUB is pointing to the incorrect location in the
root= part of the boot line, or when the hard drive has problems.
If you failed to comment out the
hidemenu command in
/boot/grub/grub.conf, press the
esc key when GRUB starts to bring up the boot menu. Your older kernel should be listed there, and you should be able to boot it. (If you can't boot the older kernel, start suspecting a drive failure. From the
linux rescue CD, try running
fsck on
/dev/mapper/VolGroup00-LogVol00 (unless you've changed the Fedora default LV names).
Do not run fsck directly on a partition (e.g., /dev/hd??) containing a logical volume. Doing so may cause unrecoverable damage to the data in the logical volume.)
Compare the
root= section of the
kernel command lines for both kernel versions. They
should be the same. If they
aren't the same, see what happens when you make the newer entry the same as the older one.
Good luck.
<edit>
I just realized you're running a XEN kernel (from your "Distribution" entry). That kernel is intended for people who plan to run, simultaneously, several different distributions. Forgive me, please, if this is not correct, but, from the tone of your question I'd assumed that you were a fairly unsophisticated Linux user. If that's the case, you might wish to review the reasoning that lead you to opt for a XEN kernel, and, if you don't really intend to run multiple distributions at the same time, perhaps installing a standard kernel would be a better solution for you.
By he way, as far as I know the XEN kernel will
not let you run Linux and Windows at the same time on the same hardware. And the Microsoft EULA for Vista
forbids running Vista on any "emulator." (That's because MS's Vista system needs direct hardware access in order to degrade your system performance when you have any "protected" media on your system for which Vista can find no license in your system's local encrypted license data base. The one to which you, as the system owner, have no access.)
</edit>
