Since it is an older computer, your new hard drive may be too big and the BIOS may not see it due to its immensely large size. Do you have Windows 95 or 98? They can only see a hard drive that is so big. I forget what the maximum is, but it's not much. I want to say 32 gigs. Here is a loophole you can try to fool your computer with, although it is a pain in the ass. Partition the hard drive, with Fdisk, into lots and lots of small partitions. Use your remaining drive letters (Probably E-Z) and make lots of partitions that are small. The BIOS will not see one BIG partition, but will see several SMALL partitions.