They shouldn't both work. One should say "not compatible with this OS" or words to that effect.
Unfortunately, whichever is appropriate to your OS (Control Panel > System should tell you what you have), they are both prone to the same (MS) design flaw. If HDD errors are preventing the OS from booting, they can also prevent the CD from booting too (It checks the HDD as it boots).
You can however use an OS which doesn't check the state of Windows first, and salvage your personal data like this, before you "factory reset" the PC