This isn't JUST a Premiere issue, but it's going here as there's no option for "this problem is with multiple apps."
My computer IS capable of GPU acceleration. I use it all the time on Premiere and Photoshop. However, whenever it FEES like it (so about once a week), something changes the user_Settings file and turns it off. I delete the file, and it works again. A week later, the file has re-spawned so to speak, and GPU acceleration is turned off again without any prompting on my end.
I'd like to know how to stop whatever it is from modifying my settings (which I leave on defaults, except for the number of history steps in Photoshop). I fail to see a reason why this would happen, and I have no idea what app is doing this in the first place; but I only use Photoshop, Premiere and the Media Encoder, never changing their settings.
Don't tell me to update, 'cause I'm on a Windows 7 machine and have no intention of changing this. My drivers are up-to-date, it's certainly NOT a hardware issue.
Unfortunately, it cannot be fixed anymore (software-configuration-wise). Microsoft had completely ended all support for Windows 7 this past January 13, while it had effectively ended feature updates and fixes for that OS way back in 2015 when it transitioned from mainstream support to extended support.
And how much VRAM do you have on your current graphics card? If your graphics card has too little VRAM, the programs that rely on GPU accceleration will switch inexplicably to the software-only mode whenever the card's VRAM gets depleted, and remain in software-only mode for the remainder of the render job.
Unfortunately, you cannot really upgrade the GPU to a newer one with more VRAM: Anything from Nvidia that's newer than a GeForce 10 series (Pascal) requires Windows 10 just to function properly. The GeForce 10 series was the last series of Nvidia GPUs to officially support Windows 7 and Windows 8.1; everything newer requires a recent build of Windows 10. With Windows 7, newer RTX GPUs will display an image, but it will be semi-permanently be locked to a fail-safe display mode using the Microsoft basic video driver. Plus, Nvidia had ended all 32-bit Windows support in 2018 with the last release of the 390-series driver branch, version 391.35, at the end of March of that year.
For AMD, Radeon GPUs will continue to support Windows 7 for the time being. However, Windows 32-bit support ended completely with the Rx 200 series GPUs that dated back to 2013. Beginning with the Rx 300 series in 2014, 64-bit Windows is required.
I have 2 GB of VRAM as far as I know, running an AMD Radeon (driver says R6). I'm NOT runnig a 32-bit system, if I were, Premiere wouldn't have installed in the first place. (I tried on an old PC, that's DEFINITELY not a thing).
This problem isn't in Adobe software itself. It must have been third-party software which may have been required to run in the background whenever Adobe software is running that's been messing around with the settings and preferences file.