Download and run GPU-Z, and see if it reports anything strange, like the PCI-E link set to x1.
Check Task Manager, see what, if anything is eating away at the CPU cycles.
If nothing untoward is found there, check your system RAM through the Control Panel>Performance and maintenance>System Will show how much RAM Windows thinks your rig has.
Update your AV software then do another full system sweep in Safe Mode.
If all is still OK download the latest sound, video and motherboard drivers then Uninstall them and then use Driver Cleaner or Driver Sweeper in Safe Mode to clean them out before reinstalling.
One word of caution, the driver cleaner software is not perfect, check EVERY item it is going to delete and deselect anything that looks wrong. It is easy to rerun the software and delete something later but much harder to replace a missing system file it deleted my mistake!