I'm having this same problem with a Gateway G6-450.
I had Red Hat 9.0 installed on the system and I tried to upgrade to Fedora 2 Core. During the first disk of the upgrade, the system rebooted and gave me a grub prompt when it came back up.
I then tried to do a full install of Fedora and it reboots during the third disk, again leaving me with a grub prompt when it comes up.
I've used the Fedora install CDs before, so I know that they are valid and it's the same hard drive that I was running RH 9.0 on so I know that's good too. Just to double check, I've re-installed RH 9.0 and it works just fine.
I've found on http://www.fedorafaq.org/#installreboot
that if you "either have an ASUS P4P800 motherboard, or a VIA C3 processor" then this problem is known and can be resolved. But I've double checked the specs on my PC and I'm running a P2-450 on a Jabil BX Motherboard. So I don't think that's going to help me.
Any help on this one would be appreciated. Thanks.