my computer derping

for a while now my computer has been stuttering and skipping at times esp during video playback (makes it hard to make mmd videos) and even testing my flash games.
I’ve basically tried everything minus a few hardware checks. I have a windows 7 machine with old nvidia gtx 570 graphics card

blew out computer and fans
did the virus checks, ran superantispyware, cccleaner, malwarebytes, combofix
deleted extra unused files/games on drives that takes up a lot of space.
ran memory tests (everything is fine)
my computer does scheduled defrags every wendnesday like at 3 am.
turned off windows event logging
no process is running that takes up lots of ram/cpu
tried latest graphics card driver version and also tried rolling back a few graphics driver versions

The computer has to be at least 8 years old or close to it so it may be time to just get a new one. So I was going to do that soonish.

Getting 4th gen i7 w/ gtx 980