Install both HWmonitor, and, CPU-Z.
Run HWMonitor.
Run CPU-Z, selecting 'Bench' tab, and then selecting/clicking on 'Stress CPU' for 6-7 minutes.
Note clock speeds and temps in HWMonitor....(Just looking to see if normal boost/turbo speeds are hit/sustained, with no evidence of throttling/overheating, etc. Being stuck at 800 MHz for example could often mean botched/over-written/now generic chipset and/or GPU drivers....)
You might also try accessing your restore points, choosing one from 7 or more days ago to see if things return to normal...; if so, then, clearly something was botched with a new driver or WIndows update combination, but, will await words before deciding how to proceed afterward...