Here a list of things to try :
-from Device manager scan for new hardware
-in device manager>view tab, click "show hidden devices" and delete all usb entries and hidden devices, reboot and test
-then you can download the latest drivers for the chipset, and reinstall it to update the USB root hubs
-start>run>diskmgmt.msc check if the usb devices show up in disk management, then run : start>run>services.msc
In the listing look for removable storage service.
If it is set to Auto, and not started, then start it : click the Start link in the top left...
-In c:\windows\inf, look for usbstor.inf - If it is not there, you can copy it from another PC..When you find it, right click it and select Install