My Laptop has problems?

I have a HP Pavilion dv7-2173cl Entertainment Notebook PC, up to recent events the laptop had been working perfectly fine, but all of a sudden when I try to start my laptop, it shows a message Boot Device not found, I would restart my laptop over again and again and once every while I would get to my loading page and when I input my password it would take a long time to get in and after a few minutes the Blue screen would pop up and/or take me back to the boot device not found error, I try to use the system recovery but when I do it would work for a bit and then repeat the boot device not found error, I also tried to re-install my Vista program but when I do i get an error, I tried to reformat the Hard drive and while it is doing so, the hard drive disappears off the page and says device not found, what can i do to fix this? I need my laptop for school