Having other operating systems installed should not be a problem. I did a google search on '/sbin/loader' and found many different problems. The most common seem to relate to the quality of the installation cd. I suggest that you run md5sun on the cd, and compare the result to the md5sum at the website from which you downloaded Fedora.
If the md4sums do not match exactly, you should then check the md5sum of the .iso you downloaded and compare it to the md5sum at the website. It it does not match exactly, you will have to download it again. If the md5sum of the cd does not match exactly, and the md5sum of the .iso you downloaded is good, then burn another cd.
If that does not solve the problem, point your browser at www.google.com/linux
, search phrase '/sbin/loader', and read about other people and their attempts to solve the problem.