Something i just stumbled on.
(In the on-line docs (GX520 Desktop User's Guide), you have a small outline computer without a lot of extra space. The documentation shows that you have one SATA port and one PATA/EIDE channel. The single SATA port is for the hard disk drive used for the system drive in this machine.
The EIDE channel will support two drives, but if you didn't order it that way you may have an IDE ribbon cable having only two connectors, one at each end for the motherboard and for the DVD/CD ROM drive. If that is your situation you will need to purchase a three connector, 80 conductor, ribbon IDE cable from a local shop or one of the on-line vendors. The cable should have a blue connector for the motherboard, a gray connector in the middle for a slave drive, and a black connector at the end for the master drive.)