Question GPU performance spikes to 0%

Dec 22, 2019
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My PC had been semi idle for about 4 months and without internet connection. After booting it up again and updating the drivers, most of my games still wont run smoothly and the PC itself is way slower than normal.
After doing some research I discovered that my GPU seems to be having some problems. When idle its always at 0% (dunno if this is normal) and when playing some games, like LoL, its spikes constantly to 0. games like Hearthstone run perfectly fine.

I read that this could be due to the GPU not getting enough power from the PCU, but after looking at the voltage, its seems like this is not the case (see graphs View: https://imgur.com/WraxT1R
)
GPU: AMD Radeon R9 390

What else could be causing this and how to solve it?