Question : Problem: Certain CD's not being detected

Hello, I have recently purchased a new computer (put together by a friend and I) and i am having a problem with the detection of certain CD's in both the DVD (an MSI 16x DVD-ROM drive) and my CD-RW (a lite-on 16x10x40 drive). The CD's are the Civilization III: Conquests and Prince of Persia: Sands of Time CD's - when I go to start both games (which are both the original CD's) the games tell me that the CD is not in the drive when it most definitely is. The conquests CD ran on my old computer, and I even took the CD-ROM from that computer and put it into the new one, but the games still don't work - I think that the problem must be with the configuration of the new computer, rather than the drives themselves. I am running an Athlon 3000XP+, 512MB RAM, 120GB HDD, Gigabyte GA-7N400 Pro2 MB, Powercolor 9600XT Video Card. I've tried all the obvious things - reinstalling the programs, installing from both drives, trying to start the games with the cd's in both drives, but nothing seems to work. Help would be MUCH appreciated!
(Sorry about the length of the question, but I try to give all relevant information!)

Answer : Problem: Certain CD's not being detected

Hi, thanks for your responses but I've fixed the problem. I changed the drive access mode from "Multi-Word DMA2" to "Ultra DMA2 - Ultra 33" and the CD's are working now (??). I'm surprised I didn't try that earlier, but I was wondering will this have a significant effect on th operation of the DVD drive, or will it be pretty much the same as normal (I don't use the drive intensively, just for gaming etc...)? Thanks again.