I agree, sounds like a hardware problem rather than your disc. Check to make sure that your CD Rom's IDE cable is connected securely on both the motherboard and drive, and in the correct orientation. Check power connectors too, they can come loose if you're in and out of the machine.
Also, if you haven't, set the ROM's jumpers to master, and place it on the connector furthest from the motherboard (end of the cable). Reset the bios (cant' hurt) and see what happens.
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