I can press ctrl-alt-f2 and log in and also ssh from my other machine, but once in I don't really know what to look for. I have booted once from the live-CD and did some kind of disk check (it was called something like smart-check) using the gui. It found nothing strange.
actually, the F15 boot may be running a filesystem check when it "appears" to hang.
Fedora 15 switched to using systemd to boot the system, and the version on F15 didn't put out a status message when it was checking a filesystem, so it appeared to "hang"
Try letting the boot sit there for a few minutes and see if it gets past a the filesystem check and continues booting.
Or you can do as Gareth mentions and run a manual filesystem check on the drives from a livecd.