Hard drives need maintenance. Clearly, since you haven't had a working drive for a long time, you haven't been doing that. Most likely the drive is just corrupted, and needs to have DiskWarrior run on it, but you need to boot from CD to do that.
I suggest you buy a cheap used CD-ROM drive for it to replace the broken one, then run DiskWarrior on it.
tooki
P.S. Dead PRAM battery would lead to a black screen, not a blinking "?".