I assume you are connecting from the PC to the monitor with a USB lead? As from looking at my Dell, it only acts as a USB hub. Unless it connects to the PC in another way?
If this is the case, can you try the port on the machine that has the USB lead that goes to the monitor, to see if it works with a non-hub device?
Hi - a "light bulb moment" - I used to connect with a USB lead as well as the monitor lead. When i set up the new PC (with Windows 7), I neglected to connect the USB lead, just did the monitor lead.