Graphics Cards

[CaptainSatire]

So I've had my 5700XT for a couple of years now, play around with very little with it, run it pretty much at stock speeds with some very light overclocking for certain games through Adrenaline profiles. Recently, however, I've noticed that sometimes my clock speed will get stuck at about 2000MHz, even at idle, when this happens, any game/app launched will do so with slideshow framerates and will be totally unplayable. This can happen in game during a match, at startup, or seemingly randomly doing any other task. The only "fix" I've found is to turn the entire PC off at the mains and at the PSU and restart, this tends to fix it for a few hours, with clock speeds then sitting around the 65MHz range at idle, but it always occurs again eventually. This has been happening for the past couple of days. 
I have tried reinstalling drivers and Adrenaline software, changing power plans, and BIOS settings, even tried a different card for a few hours. Temps during the high clock times tend to remain in acceptable bounds, but the card is essentially useless when this happens. Any advice/tips would be much appreciated.

[Venderhain]

1. You mentioned trying a different card for a while. I'm curious: What was the outcome of that?

2. When you update your drivers, do you use a utility like Display Driver Uninstaller or AMD Cleanup Utility  to remove the previous driver? Also, do you select the Factory Reset option when installing the new driver?

3. If yes to #2, do you have another drive you can boot from? Can you try a fresh Windows install or a Linux Distro? Or did you try a fresh Windows install already? This would help us determine if the problem is specific to your graphics card or if it has something to do with your Windows installation.

4. Do you remember a previous driver installation when you did not have this problem? Could you try reverting to that driver for a while?

Assuming none of the above work, I would:

- Send your card in for service with a detailed report of the behavior.

- If you don't have the money to have your card serviced (I assume it's no longer under warranty), it is possible that your GPU BIOS has been corrupted. You could try flashing the BIOS yourself. I would only do this as a last resort and ensure you watch and read a ton of content about how to do it right before attempting it. Flashing the wrong BIOS or messing up the procedure can brick your card even worse. Again, I would only do this if you've tried literally everything else and just don't have the money to service or replace your card.

[CaptainSatire]

The alternative card was an older NVidea GPU, worked fine. Unfortunately that doesn't really help narrow down if its a driver or hardware issue, and was borrowed from a friend so had to go back after a few hours.
When I update drivers I tend to just install them using the Adrenaline/AMD software and leave everything at default, never used a Display Driver uninstaller or Cleanup utility, will give this a go. 
I could dual boot/select a new boot drive if need be so Ill be sure to try that.
Thanks so much for your suggestions, Ill let you know how I get on.

[CaptainSatire]

Update, having dug around in task manager for about an hour or so I found a process called MSIexec.exe, which seemed to be causing the compute 1 module of the GPU to be at 100% utilisation at all times, having suspended this process my clock speed immediately went down to acceptable levels and performance seems to be stabilised.