Need help with corrupted Windows 8

[k_c-d1965]

 My mother's Windows 8.1 has become corrupted and we need to fix it. Problem is she has no idea what her product key is. The packaging from the computer is long gone, and it isn't anywhere on her tower. Also, we can't get into her computer because we tried doing a system restore and when it booted back up we got the following error:
"ACSTray.exe - System Error - The program can't start because rtl120.bpl is missing from your computer. Try reinstalling the program to fix this problem."
There is no way we can do that because the error message won't let us past that screen.

I looked up info about how to refresh your pc, but you have to have a boot disk. The Microsoft article stated:
"If your PC came with Windows 8.1 or Windows RT 8.1, you’ll need the discs or thumb drive that came with your PC. Check the info that came with your PC to see if your PC manufacturer provided these discs or media."

If it helps, I have Windows 8.1 on my PC and I could make a boot disk from mine, but would that work if I have a different product key? Can you use the same product key on 2 computers?
What do we do?

[y2ken]

You can Reset or Refresh your computer by following the instructions in the link below.

Refer to the section "Resetting your computer when it will not open to the start screen".

But instead of choosing RESET choose REFRESH so you don't lose your data.

Click this link: Resetting Windows 8

If you found my answer helpful please say thanks by clicking on the Thumb's Up icon.
        If my answer solved your problem please mark it as the Accepted Solution. Thanks!

[k_c-d1965]

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@y2ken wrote:

You can Reset or Refresh your computer by following the instructions in the link below.

Refer to the section "Resetting your computer when it will not open to the start screen".

But instead of choosing RESET choose REFRESH so you don't lose your data.

Click this link: Resetting Windows 8

If you found my answer helpful please say thanks by clicking on the Thumb's Up icon.
        If my answer solved your problem please mark it as the Accepted Solution. Thanks!

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And that will repair the corrupt OS? We won't need a boot disk or product key?

[y2ken · Accepted solution]

Yes, that is correct, you won't need a boot disk or product key. 

The following list shows what happens when you refresh your computer:

• Your files and personalization settings such as libraries, user accounts, and desktop themes are saved.
• The computer settings are returned to the defaults.
• Apps from the Windows store are reinstalled, and the settings are reset to their defaults. Internet connectivity is not required to reinstall these apps.
• Desktop apps are removed unless they were installed by the computer manufacturer. At the end of the refresh process, an HTML file called Removed Apps.html is placed on the desktop with a list of the desktop apps that were removed.

 This is what happens when you use Reset your PC:

• Your personal files such as libraries, personalization settings, user accounts, and desktop themes are permanently removed.
• The computer settings are returned to the defaults - the way it was when it came from the factory.
• Apps and other software that were installed on the computer when it came from the factory are reinstalled, and their settings are reset to the defaults.
• Software, apps, programs, and everything that you have installed or saved on the computer are permanently removed.

If my answer solved your problem please mark it as the Accepted Solution. Thanks!

[k_c-d1965]

Thank you for your help!

[y2ken]

Glad I could help!