If you download and install AVG antivirus free version, you can get a fully functional trial of its PC Performance software for a month, I believe, that will find and fix a host of issues and registry problems. It is as good or better than many commercial products like Registry Repair Wizard.
When it is done, you just remove it, though the antivirus software is still good if you like AVG.
On an older system, I wouldn’t be surprised if it found more than a thousand mostly minor problems. But that stuff adds up.