My guess is that you hard drive has failed. If you enter the BIOS setup does it detect the hard drive there? If not you can try removing and reinserting the hard drive and if that fails then you can try the drive in another computer to see if it gets detected and if it's accessible. If it doesn't get detected in a second computer then it has failed and will need to be replaced. And you've also lost everything on it unless you had a backup.