Acrobat Pro v8 crashes as soon as I open it

It's probably crashing because Adobe took down the activation & registration servers years ago.  At one time, there was an activation free-installer and replacement serial number program.  But Adobe recently ended that program.  So as it stands today, Acrobat 8 is officially dead & gone.  There is no possible way to re-install and activate Acrobat 8.   

Acrobat Reader DC is free.

https://acrobat.adobe.com/us/en/acrobat/pdf-reader.html

If you need more than that, Acrobat Standard costs $12.99/month for 1 year.  Acrobat Pro DC costs $14.99/month for 1 year.

https://acrobat.adobe.com/us/en/acrobat/pricing/compare-versions.html

Acrobat 8 is a version that has been around for quite some time, and has not been certified on Windows 7.
And Windows 7 will soon be out of support.
We recommend you take this opportunity to migrate to Windows 10 and Acrobat DC.

Acrobat 8 is extremely old and not compatible with any current operating system, not even with Windows 7. I'm afraid that such problems are to be expected. Your best chance of getting it to work is to update Acrobat 8 to the latest available version and run it in Compatibility Mode with an earlier OS, and even then it might not work...

Can you tell if an unattended update took place in your Windows 7?

If you are certain that you have exhausted trying  the usual troubleshooting guidance for that old version of Acrobat try the following:

• Verify if during an unattended update the default PDF ownership wasn't  assigned to a browser or another third-party PDF viewer instead of your Acrobat
• Verify that if you have installed the new version of the Reader DC disable or remove it (for troubleshooting purposes),  OR, see if this works; go to this direcctory C:\Program Files (x86)\Adobe\Acrobat Reader DC\Reader  and search for "Eula.exe".  Double-click to open and accept the agreement. Then click OK to close. This doesn't make sense as it applies to the Reader DC but is a windows trick that apparently gets rid of runtime errors associated with the Adobe Reader.
• Use the built-in feature "Restore From Previous Version" on your Acrobat .exe launcher (do not confuse this procedure with System Restore since it's not the same as System Restore). See short video here:  https://www.youtube.com/watch?v=2jmJ27s-ZVA
• Verify that the program is not blocked by the operating system. You can try and disable Data Execution Prevention for that particular program or all programs. See how to here: https://answers.microsoft.com/en-us/windows/forum/windows_7-security/windows-security-blocking-file-execution-how-do-i/772ff4c0-b3ea-4862-995e-5942a419bd67
• OR, manually unblock the program http://freewindowsvistatutorials.com/unblocked-blocked-programs-in-windows-7-zipped-or-not.php
• Check for 32bit vs 64bit compatibility issues. According to old threads both Adobe Acrobat 8 and Windows 7 are not compatible. If you are one of those who were able to make it work before refer back to this guidance: https://community.adobe.com/t5/acrobat/acrobat-8-and-windows-7-don-t-work/m-p/4465005
• If else above doesn't resolve your issue, then try a System Restore

NOTE: It is possible that an activation service was triggered during a system update. Be advised  that Adobe retired the activation servers for that old version.

Last, see if this works:

• In MS Windows, usually 32 bit apps are installed here: C:\Program Files   while 64 bit apps are normally installed in here: C:\Program Files(x86)    Re-verify in which directory you're trying to force the setup program.