That sounds as if the laptop is having difficulty supplying enough power to the scope. When that happens the laptop will shut down the port. If it is a 320x series scope, try using the supplied external power supply. If the scope does not work on other laptops and PCs, please contact us on Help-desk to have the scope sent back for repair. It it is the laptop, we cannot help, probably the reservoir capacitors in the laptop have dried-out, reducing the peak current available.