What should i do when my window 7 not detecting usb

Try this:

1) Run the fix it from “Hardware devices not detected or not working”
http://support.microsoft.com/gp/ha [...] e_problems

2) Then refresh the USB Stack
a. Click start-Control Panel - Device Manager –

b. Expand USB Serial Controllers - RIGHT CLICK on EVERYTHING and UNINSTALL all except the category itself.

c. REBOOT the computer. This refreshes the drive and the USB stack