This can happen if the drive can't read the disk. Things that might help:
- Reburn the disk (cd-r, not cd-rw)
- Use lens cleaner
- Replace the drive (they aren't expensive)
Of course, it can also be a motherboard problem. But you didn't tell why you needed a rescue disk, so I started with the common cures.
I can't get my PC to boot from CD even though the bios is set to boot from CD as 1st priority. In fact I changed all 3 boot devices to CD-ROm and it still boots from the hard disc.
I am trying to boot from a rescue disc which works ok in my laptop.