For your sparc system, check which of the Solaris 10 releases are supported first.
Also do a upgrade of the OBP(recommended). If both is done, and its still not working, possible to be a dvd problem... did you just try to boot off other solaris installation cd/dvd?
try a probe-scsi-all from the ok prompt. then do a show-disks and you should see your cdrom in the list, if you do not see it then the obp is not recognizing your cdrom drive. if you do see it you should then be able to devalias and see the path to your cdrom in show-disks is aliased to your cdrom. If it is not, or the path is wrong you can then do a
nvalias cdrom1 /dev/.../.../.. this will set up a new alias for the path to your cdrom known as cdrom1.
and then boot cdrom1 and you should be good.