OK, please do the following.
Step#1 - ChkDsk Repair
Assuming you are still at the command-prompt window I would like you to do the following.
1. Please type the word notepad in the black command prompt window and hit Enter on the keyboard.
2. Under the File menu of notepad, please select Open.
3. Double-click on Computer and then identify which drive letter represents your Main hard drive. It won't be or X: and it should show a size of around 290 to 300 GB.
4. Click Cancel on the Open Dialog from notepad and close notepad.
5. In the Command Prompt window, please type chkdsk C: /R and press enter on the keyboard. Note: Replace C with the Drive Letter you identified in bullet#3.
Note: There is a space before the /R and a space after chkdsk.
6. Chkdsk should begin to run. Let it complete.
Let's try re-booting your machine and see if it will come up.