USB ports not recognized at same locations every time. Work everywhere else! What would cause this? [View all]

I work at a number of schools and have found that every time I work at the same three schools, my USB ports stop working. I get a message that says they are not recognized. They work everywhere else! I even turn off my wireless connection before I get to these schools and still get the problem!?!? What kind of electronic signal would cause a USB port to stop working? Is there anything I can do to combat this problem at these locations?

PS. I have tried rebooting at these locations and shutting down for at least five minutes but it does not fix the problem. I go to the next location and everything works perfectly! My co-workers computers don't have this problem. Mine is a Dell Inspiron with Windows 7. I believe everyone else has Dells too as they are provided by the company. Mine is even a more expensive one that most of the other workers have.