I just installed Windows 10 on a z820 and I'm having USB issues. I came across this (https://support.hp.com/us-en/document/c03291465) which explains the issue of the cursor lagging due to interference from a thumb drive below the mouse (Logitech M705) receiver in a usb 3 port on the front.
What's weirder is that the USB 2.0 ports on the front and back don't work at all and don't provide power to the wired keyboard or receiver. They also don't cause a notification sounds like the 3's. Any ideas?