Are you trying to play them from WMP or Explorer? If they don't play by selecting them through just WMP, then try opening them in Explorer as it is likely the file location is slightly different.
If they don't play when double clicking on the ACTUAL file, it is indeed most likely a codec error. If I remember rightly, basic WMP only lets you rip to wma, mp3 and (possibly) wav format natively. It should be able to play those files back.
Try opening the files in
VLC as it plays
nearly all audio and video formats going. (It comes with a load of codecs by default so it'll probably work to be honest)
If VLC doesn't play them, there may be something corrupt / not quite right with the files themselves.
If the discs have copy protection on them, WMP may have decided to stop you from playing them correctly (by requiring some kinda DMA-type license thing). Try ripping them with some other software such as
iTunes or
FreeRip (I used to use it "back in the day")
If THAT doesn't work, try playing the discs normally through WMP... Try playing them in a CD player... Just do everything possible to make sure the discs still work normally.
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