I think he ask for "scan for hardware changes" as he said,
"have introduced an 8GB disk.
I have it connected to my tower but nothing happens"
Go to device manager through,
start-->search-->type "device manager"
now plug the 8gb usb and now check any changes happen there or you see any yellow exclamation mark there?..
Also try to search in Disk management,
click on Start and then Run.
Type the following command in the text box:
...and then hit the Enter key or press the OK
now did you see the usb there?