Upgrading to Windows 10 or 11 would be your best option. It's still free by Microsoft. Windows 7 isn't supported by current OBS any more. You might try older OBS versions, however there is no support for these in the community any more. OBS has evolved so much since then and addressed so many of these "black screen" issues since the last version that was able to run under Windows 7, it's no use to keep obsolete support information alive.