Your challenge is to figure out what you changed on your computer, since the program obviously hasn't.
First, manually go to Windows Update and ensure you have all -- even the non-critical -- updates.
Then ensure you have the latest version of Quicktime from Apple.
Then do some cleaning and tuning. My personal favorite tune-up program is Advanced System Care from iobit, which does a Deep Clean and tune with a single click of a button. And it's free! I've used it every week for yearsand my 6 year old computer runs better than when it was new.
I know your computer is virtually brand new. But, trust me, it's still full of junk files and fragmentation. And quite possibly malware. (And, if you're running Norton 360 -- well, a lot of people consider IT malware, the way it eats system resources.)
You should also go to Premiere Elements' Edit/Preferences and clear your Media Cache.
(And, for that matter, go to your Internet browsers and clear their caches. You'd be surprised how much junk in your browser's cache can slow down your computer!)
First take a look at these and provide the info requested in the first link (source, format, project settings, how clips were imported, etc...):
I have not made any changes to my computer, other than moving it's location (I moved to the well ventilated Den).
It may be worth your while to take the lid of and make sure that all your internal boards are properly seated.
Insanity is hereditary, you get it from your children