Boot disc not recognized

We have a “just out of warranty” Acer Aspire X1200 which will not recognized boot discs. I have checked the Boot Sequence in the BIOS and it is correct, but I’ve tried 3 different bootable CD’s and the machine will not recognize the boot function on the CD. I’ve tried 2 Windows XP CD’s and one Ultimate Boot Disc CD, all of which work on other machines.
Because the machine is fairly new and other CD’s work in it, I’m stumped and would appreciate any help you can give.
Thanks