Try safe mode (power on - press F8 before the windows splash screen), if that works, then try rebooting normally.
If you still get the black screen, chances are a recent install is bad, go back into safe mode, and then start deleting your last software installs.
You can also run malwarebytes MBAM from safe mode.
You can try restoring to an earlier point from safe mode.
If you can't access it at all, chances are that you will need to run the restore CD or boot from the utilities partition and do a factory reset.
This will wipe ALL the data and make the machine basically as it was when you purchased it, so if you have any critical data to be copied, you'll need to yank the HDD and throw it on another system to backup your docs.
On a good note - if you can get as you have, all of your data should be accessable, it does not sound like a hardware failure.
Not much more I can recommend without knowing more, good luck!