On an old PIII 800 system I have the boot up goes VERY slowly and hangs all the time. I found out it was because the Floppy drive was no good, I unplugged the cables to it and the system booted up just fine.
Best thing to do is to put the Seagate into another computer as a slave and see if you can pull any files off of it. Usually there are signs a HD will fail, like a shrieking noise or just piss poor performance. There are utilities
here that should be able to tell you the condition of your drives.
Good luck, losing your main HDD is never fun, which is why more and more people are cooling their harddrives and/or doing RAID 1.