Monitor USB ports stop working after power down

I have the Dell 17" UltraSharp flatpanel. I have the USB cable hooked up to my monitor and computer, and all 4 ports on the monitor work fine, that is until i turn the monitor off. If I turn the monitor off, then turn it back on, the USB ports no longer work. This is very frustrating because this is where I plug in my keyboard and mouse, and they will not work after I turn the monitor off.