[TriLUG] strange boot problem

[Merle Watts]

tying to boot a computer from cd or dvd.   It will boot from a windows xp cd and a knoppix cd.  will not boot from a manfrake 10 cd, mandake 
9.2 dvd, or a fedora dvd.

this is happening on 2 different computers
I get an error that says to put in a system disk

one of the computers has had an install of mandrake 9.2 and fedora using the dvd's  that will not currentl boot.
I am writing thiis on the one that is running fedora that was installed from the dvd about 3 weeks ago

all of the above disks will boot fine in my laptop.

any ideas

Thanks