As I was putting the saw blade on my new Ryobi Circular saw my finger slipped off of the blade lock button while tightening and now I cannot get the blade lock to engage again. What would be the fix for this?
You can probably use a screwdriver between the teeth of the blade and the guard to prevent the spindle from turning while you wrench on the nut. I bought a used miter saw a few years ago with a broken spindle lock and this is how I change the blade on that. If it's under warranty, I wouldn't recommend you try to fix it yourself, and instead send it out for repair according to the manufacturers' guidance.