It's either a failed hard drive or a failed motherboard. Or somebody deleted the OS from your hard drive. Boot into a Linux disc or stick (free to make) to look at the disk.
I have a problem with my hp pavilion dv6000 laptop in which it fails to start up with the display remaining on the "HP INVENT" screen. It later goes blank and shows that the operating system is not found and the media test failed. Is this a hard drive problem that I need to replace? Please help & Thanks in advance kind people!