How to check, if USB stick is broken (as well as USB ports)?

We want to open up an USB stick. When putting it in the USB port it will not open the data (no reaction at all). We tried the other 5 USB ports. Same problem. We checked the USB ports, but they all show they should work just fine. Now, we are just baffled. Any advice or suggestions? Is there a USB stick tester (to test if USB stick is broken or not) on the market?