I was getting read failures (CRC errors, or sometimes just looping read errors) from files on a number of old DVD backups. The failures occurred consistently on two different PCs. Because the DVD drives in both PCs were a few years old and both had been used heavily, I purchased two replacement Plextor PX-870A drives in the hope of recovering the bad files. I installed a new drive in each PC.
Miraculously, all copy operations which previously failed were now successful on PC1. However, the same file copies failed in the same ways on PC2. In an effort to troubleshoot the difference, I swapped the two drives between PC1 and PC2. The result is the same -- a file copy succeeds on PC1 but fails on PC2. On PC1, the Event Viewer shows only a handful of read errors, but on PC2 there are many, many read errors and the copy operation either fails with a CRC error, or just goes into a loop of read errors and has to be cancelled.
As far as I can tell, the drivers on both PCs are the same. Windows XP, Service Pack 3, on both PCs. Thanks for any suggestions on what might be the difference between the two PCs, or places to look in an effort to troubleshoot.