About 3 years old - I did have a crash on New Year’s Day due to a power failure and it acted weird for a week or two after but seemed to fix itself and was fine until now. The funny thing is that my old computer did the same thing after a Windows 98 update and it neevr would run 98 again. XP would work fine though.
It wouldn’t hurt to try that Firefox Flashblock add-on that I mentioned. Your problem sounds a lot like what I went through. I tried all the major browsers and they all had the same problem. Disabling the automatic playing of Flash is what finally solved it.