HP Laptop "Operating System not found." and Unable to boot CD/DVD's
 

Fixed.

I'm not an expert so don't take my advice as fact. Also try posting this on a more tech related forum. Not sure if I can mention the forums I use due to the rules, but just Google something like Tech Help forums.

Anyhow, it sounds like your BIOS isn't reading your hard drive. When you go the BIOS menu, IIRC, you can check if your hard drive is listed. Google how to exactly. If your BIOS sees the hard drive, it is likely a problem with the hard drive itself. That's all I know on the subject, sorry.

I know my hard drive is detected as I can do the Primary Hard Drive Self Test with success with my new hard drive, which my old hard drive couldn't.