I have a Dell Latitude E5570 running Windows 7. There are three USB ports on the laptop (one on the right hand side and two on the back) and when I connect my keyboard and mouse to them they work fine.
However, when I attach the laptop to the Dell Dock (I think its the Dell Advanced E-Port 2) is when I get problems with the USB ports. The USB port on the side of the laptop works fine. The two on the back of the laptop stop working. None of the USB ports on the Dell Dock work.
I have two monitors attached to the dock and they work fine.
Odd thing is that they seem to work when the system is first powered up as the laptop is protected by some sort of device encryption (???) and I can type the password fine. I'm assuming this is a Windows issue.