Have you tried booting up the disk themselves and seeing what comes up, most disk in a series are able to boot but then will request that you put in disk one and start again, if these disk won't even boot up there maybe a problem is with disk 2 and 3.
Other wise it's a head scratcher.
Playstation has made disk errors before, I own a copy of Castlevania
Greatest hits - when you pop it in to play, ta da, it comes up as Elmo's Letter adventure!!
