are there leds on your usb sticks? if so, do they light up when you insert them in the usb slot?
is usb enabled in the system setup/bios of your motherboard?
is the energy saving settings disabled on each usb device in your operating system?
do you get the recognizable sound when you insert a usb stick?
how many drive letters does your system have? are there card readers inside your system clogging up drive letters? can you assign a new drive letter to your usb device?