There would be the following two possibility:

1. Power supply issue. You can connect the SSD through the USB port on back of the desktop to ensure the USB power is strong enough. Don't use the USB Hub or any other USB extension device to connect the SSD to the host because these devices can not supply USB power strongly enough.
2. The SSD has not been added into the OS. Please add the SSD into the Windows XP or Windows 7 by the device manager.