HELP WITH MY VOSTRO MY SCREEN SAYS" aN OPERATING SYSTEM WASN'T FOUND . tRY DISCONECTING ANY DRIVES THAT DONT CONTAIN AN OPERATING SYSTEM. PRESS cTRL+alt+delete
Press F12 a few times after the power button and boot to the Dell diagnostics. Run an extended test on the hard drive - which you will likely find returns a failure code, meaning the drive has failed.