Solved USB works for some but not for all?

Hi, this is a weird one. At the back of my comp i have 6 USB's that take things from mouse to keyboard to piano keyboard and all work. When i use a USB stick though things are different. My PC recognizes the USB and a little light comes on it and it does come up as a drive but when i try and open the USB I get the error: G:\ Application not found It is always G:\ no matter which USB...