It sounds like your hard drive has failed, or is in the process of failing.
I suggest you Boot from a disc, and run some diagnostics on the hard drive.
But you will either have to go purchase said diagnostic disc.....or use a different computer to download the diagnostics software (its free, from ultimatebootcd.com), and then burn the diagnostics software to disc, and then boot from the disc on the problem computer.
A situation like this requires a bit of know how, and its really akin to instructions, because there are so many variables and we cant account for all of them......thats why computer technicians are needed to fix the issue.
I dont want you to think that just because you get a diagnostic disc, it will fix the computer......all it will do is tell you if the hard drive is failing....which it probably is.
At that point, you have to replace the hard drive, and then REINSTALL the OS (Operating System), to restore functionality.
Then your data needs to be put back on.....but if your current hard drive has failed.....all the data that was on it.....is gone.
Unless you want to pay a bunch of money to get it recovered ($500-$1000).
This is going to be anythign but easy.
I suggest you take the machine in for repair....unless you are famialiar with diagnostics of hard drives, AND replacing them, and installing the OS.
YOu could end up spending WAY more time and money, ifyoutry to tackle it on your own.
I can help you through it thoguh.......if you want to try?
Either way......please take a moment to rate.