Did any changes to your computer prior?
If you have any unnecessary external device connected to the machine, you may unplug them & check if you are able to boot to the desktop.
a. Boot the computer to windows recovery options and select startup repair.
b. If startup repair fails, insert the Windows recovery disc and select command Prompt and type in: rename c:\windows\system32\drivers\classpnp.sys classpnp.old and select startup repair again.
You may try to run chkdsk from Windows Recovery Environment & then try to boot to the desktop normally.
a.Follow the steps from this link to boot into Windows Recovery Environment and open the command prompt.
b. In the command prompt window, type ‘chkdsk /r’ and press Enter.
While performing chkdsk on the hard drive if any bad sectors are found on the hard drive when chkdsk tries to repair that sector if any data available on that might be lost