Tip: Using a clean Mac OS installation to isolate issues +
I just wanted to remind folks on what can be a very valuable tool for anyone to employ and especially computer consultants who regularly have to work out issues.
So the idea is rather simple, use an external hard drive, USB stick, whatever, something that your Mac can boot into. What do you install on this drive? An up-to-date Mac OS compatible with your Mac. It should be a strict clean install of Mac OS with nothing added. Just the stock install.
When you are facing an issue that you are unable to resolve you need to quickly isolate the issue to one of two components, a hardware or a software issue. This is essentially what makes up a computer, a hardware and software platform working together to create the entire computing experience.
If you are not sure what is wrong with your Mac, simply boot off this standby OS, start up using it and see if the issue is reproducible. If it is, ensure that your hardware configuration is as stock (out-of-the-box) as possible. To do this simply disconnect all external hardware or any RAM or internal component you might have installed. In other words, return the hardware to as close to the original config as possible. Of course sometimes you installed an internal HD in an iMac or some other closed system and it would be unreasonable to simply open up those machines but if all external devices or user installable hardware has been removed from the hardware configuration and issues persist when booted off this stand by clean OS then ask yourself if there is indeed some internal hardware that you may have installed, it could be dying or dead or need some software fix, for example reformatting an internal drive etc.
If after booting from this standby OS everything just works as expected. Connect up external hardware reboot and test again. If things still work fine then you have isolated the issue down to the software on your main drive.
At this stage, we don't need the standby OS. Next you have to come to some reasonable best attempt guess on whether the problem (the issue) is user account specific or system wide.
To quickly find out, create a new 'test' user account and login. If the problem (issue) is not reproducible then the issue is user specific. If the issue persists in the test user account then it is system wide as it affects even this new test user account.
So based on this you will need to either troubleshoot files in your user account or files that are outside any user account.
As I noted, this post is based on another post I created. To be brief, if you are not sure how to proceed, namely what to look for, then consider downloading EtreCheck (free), launch and run it and read the report carefully. If you are still stuck, come back to this lovely forum, create a new post, introduce the issue and include an EtreCheck report.
If you have any questions feel free to ask. Hopefully this is a helpful note on general troubleshooting.