The ribbon cable is for the Hard Drive, its a ATA and if you look its not a slide connection but got pin holes on one side this is what connects to the drive. Plus there should be what is called a Moler connection this is a for pin connection socket that powers the drive and only connects one way if you take another look at the ribbon you should see that the ribbon as a red tracer wire on one edge this connect to the Hard Drive with the Red next to the Above power plug. There may be other things wrong with the PC did you get any info about it, you will also need a Operating System CD to load before you can put any software on it to run it.
This is what I would do before going further with the PC. If you know some one who will create a Live Linux CD for you, you can boot and run the PC without a Hard Drive this will tell you if the PC is any good before spending on it.
Free Linux Live CD can be downloaded from hear
You need a Desktop Insulation
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