Why will my PC not boot from SATA Solid State Drive

Why will my PC not boot from SATA Solid State Drive

I upgraded by adding a SSD via SATA port on the motherboard. It works fine but will only boot if I also have a (redundant) operating system (Windows XP) on the original IDE drive. I can then choose to boot straight from Windows 7 on the SSD. Without the IDE drive I get a boot error something like Primary Hard Drive Not Found.