I turned on my Dell Ispiron 7567 and it felt very sluggish. Then I took this screenshot:
According to Windows 10 Pro Fall Creators Update Task Manager it was running at 0.47 GHz and it wouldn't go any higher. The laptop was completely cool as I just turned it on. BTW I am running a power profile set to TDP 35W.
Even opening a folder would take a few seconds. Windows sounds were very laggy and choppy. I asked Windows to shut down the laptop and after the screen went dark. It took over a minute to turn off all lights. Fan is usually not running and I am using SSD so there aren't any other noises.
After I rebooted Task Manager agrees with CPU-Z - the CPU is idling at around 0.89GHz and everything is running smoothly as usually. CPU is going over 1GHz when loaded.
Any ideas what might be causing the throttling?
This is usually caused by an incorrect configuration setting within the BIOS. We can't help you with BIOS issues on non-Intel products. You need to contact Dell and have then look into this.