Since 2 days, my PC has been ruinning incredibly slow, I mean like nearly 1 minute to maximize a window, 30 sec+ to open the start menu. I rebooted and it worked fine for another few hours and started again.

I noticed explorer.exe is always using 98-100% cpu in task manager.

Could this be a virus? My updated AVG AV doesn't find anything, but none of the AVs I've had have ever found any viruses even when I had some, so I don't trust any AV at all since they only detect known viruses.

Could it be something else?

Thanks