siemens communication failier

hi, i have a problem to communication with siemens plc s7 200 to my personal computer, i have usb/ppi multi-master cable ,my problem when i use cable RS232 i can communicate with plc ,but when i use usb it can not communicate ,my cable no, 6es7 901-3db30-0xa0

ahmed,
your cable is ofcourse the right one.. Have you selected communications via USB port?if not,double click Set PG/PC interface(under communications bar in ur instruction tree) ---->properties---->Local connection--->Set this to USB..
If its stil not working.. then the prob mite b wit ur
* cable or
* USB port in ur system..

Sometimes version of software may also give problem. cheeck you are using version STEP7 Microwin 4.0. Then it has USB selection.
Hope this will help