Her u interrogation to the computer after the exit, insert a U disk again, found that Windows 7 can not recognize the U disk. You have to restart your computer to recognize it again. Here's how to solve this problem:
On the Windows 7 desktop mouse Right click Computer, select Properties. Click on the upper left corner of "Device Manager", followed by the pop-up "Device Manager" window, click to expand "Universal Serial Bus Control", there are many rows of "USB Root Hub" List of devices, I have here 8. Right-click each USB Root Hub, select the Disable menu, and then enable.
By doing this with each USB Root Hub, Windows 7 can identify the U disk again without rebooting.