USB cannot read barcode scanner

Hello everyone. I wish someone would take time to read and help me with my problem. You see, I have a barcode scanner. Now, the scanner that I have has a serial port. When I connect it to the serial port on my desktop, it is working fine. The problem is, I have to do the programming part in my laptop. My laptop does not have any serial ports, so I purchased a connector that will convert it to usb. I tested the connector in the desktop, all ps/2 devices (ex. mouse) works fine. But when it comes to the barcode scanner, the computer cannot read the device. Which is weird. It can read the device when I connect it to the serial port, but it does not read the device when I connect it to the USB via a connector or converter. Any ideas?