as long as the /boot is separate from the rest of the system than booting to a live cd and reading /etc/issue
or /etc/redhat-release should tell you
however if you /boot partition is really separate, you shouldn't have to re-install your whole system to fix this
what you would do is boot from a live/rescue cd
create a mount point (directory) for the / partition for my example i will use /repair
mount the / partition
mount /dev/sda3 /repair
re-format the /boot partition
mkfs -t ext(2,3, or 4) /dev/sda1
mount the /boot partition on /repair/boot
mount /dev/sda1 /repair/boot
then bind the /dev, /proc, and /sys directories of the live cd into their respective directories on /repair
$ su -c 'mount ‐‐bind /dev /repair/dev'
$ su -c 'mount ‐‐bind /proc /repair/proc'
$ su -c 'mount ‐‐bind /sys /repair/sys'
then chroot into the system
$ su -c 'chroot /repair'
if you are already running as root on the live cd than you can issue the commands without the su -c
once you have that done, you can simply use yum (or up2date if you are using Red hat enterprise linux) to re-install the packages (the kernel packages) from the repositories (assuming your live/repari cd provides internet access), or from locally downloaded copies if you don't and reinstall grub to generate a new grub configuration file
# grub-install /dev/sda
once you have this done you should have a functioning system
note, /dev/sda, /dev/sda1 and /dev/sda3 are merely examples, you should figure out which ones are correct for your system.