rollback the kernel
There is more than one way to skin a cat, but this works for me. Version 2 is easy, but Version 1 is good to know.
You can use vi as I do in the example, or whatever your favorite editor is. gedit will do the trick to.
Change the line "default=0" to "default=1" (highlighted in red)
title Fedora Core (2.6.17-1.2142_FC4)
kernel /vmlinuz-2.6.17-1.2142_FC4 ro root=/dev/VolGroup00/LogVol00 rhgb
The kernels are listed in order starting at 0. By changing this to "1" you are basically telling it to boot with the second kernel listed. After a reboot you can uninstall the kernel. Perhaps you used yum to update in which case you could use the command:
#yum remove kernel-2.6.17-1.2142_FC4 (replace with your kernel version)
As the cpu is booting press any key when you see the kernel version listed and choose a different version. Continue to boot and uninstall the kernel using yum as described above or the following command:
#rpm -e kernel-2.6.17-1.2142_FC4 (replace with your kernel version)
Hopefully these instructions are complete. I'm sure someone will let us know if they are not.