It sounds like one of your disks went bad, not that your BIOS went bad.
Why is your Windows XP CD not bootable? In my experience, all non-upgrade WinXP CDs have been bootable.
To test to see if your system can boot up, this will ensure that your BIOS isn't corrupted, burn an
Ultimate Boot CD. This is a utility CD that you can use to do various things. It will show if your system is bootable or not. Try it out and let us know if it loads.