Hello Daveb30,
I'm sorry to hear that you're experiencing issues with your computer.
When you perform the Hard Disk Check, what does it say in front of the error, such as SMART Check, Short DST or Long DST?
If you're able to enter the actual diagnostics system, and select the hard disk check proberly, the message "not installed" does not necessarily indicate that the diagnostic tests are not installed.
If it reports a feature of the harddisk not being installed, then it means the harddrive is no longer working properly, and will need to be replaced.
Since the notebook is only 6 months old, it's still covered by warranty. Contact the HP Technical support to have the harddrive replaced.
If you live in the US, contact HP through the following link.
http://welcome.hp.com/country/us/en/contact/phone_assist.html#section1
If you are in another part of the world, start at the following link, select your country and select "Contact Us" at the bottom left of the website.
http://h10025.www1.hp.com/ewfrf/wc/weInput?cc=us&dlc=en〈=en&lc=en&product=4221435&task=