Laptop won't boot Linux or Windows

I have a Latitude c810 a few years old (don't know exact date; bought it used) with Windows XP pro installed. I want to dual-install Linux on it, and borrowed the Mandrake 10.1 CDs from a friend (not wanting to mess around with LILO myself). I made sure everything was up to date, installed the latest BIOS (A12), etc. When I tried to boot Mandrake, I couldn't; it went automatically to Windows. I tried again, after setting the computer only to boot from the CD drive, but it still wouldn't boot. Annoyed, I tried Knoppix instead; again, it wouldn't boot. Thinking something might be wrong with the CD drive or the CDs themselves, I dug out some old Windows 98 floppies to see if they'd work: they didn't. I've tried everything I could think of, but have no idea what's wrong. Any thoughts?

(also posted to Latitude-bios forum)