I've erased by mistake an important library (gclib or something like that)
How is it possible? I'm not here to blame you, we learn from our mistakes, so learn that under GNU/linux, you've got a packages manager that handles softwares and libraries updates, installing and removing... The one for fedora is yum, and a GUI for it is yumex. By using yum, you won't removing a base library by mistakes, updates for every packages on your system will be automatically updated, it will deal with dependencies when installing new softwares...
By the way, I'm not sure but I think that your fedora media surely have live-CD mode, or better a recovery mode, thus you'll be able boot a system.
The idea is:
-mount your hard drive which contents "/lib" (assuming you've removed the libc)
-copy by hand the libc used by the live-CD into mounted "/lib"
-reboot on your system, hope that works
-take a look to yum to re-install properly libc with yum.
If the fedora media have a recovery-mode, maybe this kind of problem can be handle automatically...