NEC nd-3530a cd/dvd not working

Hello all. This is my first post for me as I can normally figure out what's wrong but this time I can't fix it. 

My parents have a Dell Dimension 5150 still running Windows XP - this is because that majority of the programmes on the computer can't run on later Windows platforms. Anyway, I took the tower away to my house to do some work on it and then brought it back after a couple of days. I put everything back and went to turn it on, it came up with a boot failure, unable to boot from diskette, which is strange as there is no floppy diskette installed. To get it to boot again, I had to reset the BIOS and turn off the diskette option. After it all started up again I re-upated to the latest BIOS. Not too sure If it is a coincidence or bad luck, I have found that the nec nd-3530a dvd drive no longer reads any disks. It makes some clicking noises every few seconds but doesn't spin up. The drivers were in stalled and says this device is working properly. As a quick option, I bought a second hand unit. I fitted it and installed drivers but still didn't work. I tried again and all of a sudden it started to read a dvd. I then tried an audio cd and that worked, then an installation cd and it read  that to. After a while I tried a dvd again but now had stopped working again and will not read the previous disks I tried. The second hand unit sort of makes the same noise as the original. I carried a diagnostic test and have Error Code 0F00:021B Floor in medium or an error in recorded data.

Would it be possible that both dvd drives are faulty? If anyone can help that would be great.

Dave