I'm sorry, but I've never heard of that particular computer component. Please be more specific. Are you talking about the BIOS? They don't just "go out" unless you did something wrong when plugging in the hard drive. The problem is more likely that the BIOS may not be able to detect your hard drive, especially if you purchased one that is not compatible with that particular system. What model of 5600 is it? What hard drive did you purchase?
Do you know how to access the BIOS on a Compaq? If you care to browse the Compaq site to find the owners's manual to get help for your problem, here's the URL.
http://h18000.www1.hp.com/cpq_support.html
It may also lead you to find what hard drives may or may not be compatible with the system you have. There are MANY models of 5600 to choose from.