I don't understand what you mean by a locked black screen.
- If it is password locked, we can't help you other than to say reinstall the operating system.
- When you say it is a black screen do you mean it turns black and remains that way after the original splash screen logo etc. appears when you first turn it on, or it is permanently black?
Here are the repair options in Windows 7:
What are the system recovery options in Windows 7?
The System Recovery Options menu contains several tools, such as Start-up Repair, that can help you recover Windows from a serious error. This set of tools is on your computer's hard disk and on the Windows installation disc.
Note
You can also create a system repair disc that contains the System Recovery Options menu. For more information, see
Create a system repair disc.
If you use a Tablet PC or other computer with a touchscreen, you might need to connect a keyboard and mouse in order to use Start-up Repair and the other tools in the System Recovery Options menu.
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Often a Start-up Repair, etc. disk will work where the built-in Repair Software won't
Make your own System Repair Disk from the information in this Tutorial or from the prior information:
"How to Create a Windows 7 System Repair Disc"
http://www.sevenforums.com/tutorials/2083-system-repair-disc-create.html
"This will show you how to create a Windows 7 system repair disc to be able to use to boot to
**system recovery options** to help recover your Windows 7 installation if you don't have a Windows installation disc, can't find your Windows installation disc,
or can't access the recovery options provided by your computer manufacturer.
A system repair disc is not able to install Windows 7.
Note
If you are unable to boot your Windows 7 to create a Windows 7 System Repair Disc, then you could create it on another computer to use on your computer."
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Then use that Disk for the System Recovery Options:
"System Recovery Options"
http://www.sevenforums.com/tutorials/668-system-recovery-options.html
"How to Run a Startup Repair in Windows 7"
http://www.sevenforums.com/tutorials/681-startup-repair.html
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But if you do not have access to another Windows 7 machine with the same "bit" version use this method to make a disk, from which you can also use the Startup repair options:
You can use this for preinstalled OEM or Retail Licenses. This is on a first come, first served monthly basis.
Download the correct ISO file and make your own disk and use the Product Key that is on the COA Sticker.
https://www.heidoc.net/joomla/technology-science/microsoft/67-microsoft-windows-and-office-iso-download-tool
Download: Windows ISO Downloader.exe
And here are instructions on how to burn ISO images to disk:
http://www.snapfiles.com/get/ISORecorder.html
You change the Boot Order in the BIOS to be able to boot from your installation media:
How to Boot Your Computer From a Disc or USB Drive
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These are your Repair choices:

You should now click on the Repair your computer option to start entering the Windows 7 Recovery Environment.
Which leads to these options, including Startup Repair, etc..

Cheers.