Upgrade to Windows 10. Your hardware is perfect for it. Upgrade is still free - just get the installation data directly from Microsoft:
https://www.microsoft.com/en-us/software-download/windows10
Then you're able to upgrade to the most recent Nvidia driver for best GPU support, and you're able to upgrade to the most recent version of OBS. If you stay on Windows 7, you will waste more time with trying to fix unfixable things on that old platform than you need for doing the upgrade. It will not get better, only worse the longer you delay the upgrade.