Sorry you are finding the PLM difficult to interface to. What is the configuration where com port 3 is the PLM port. Normally when using some form of USB to Serial conversion port assignments start with 4. Different port numbers can be tried. Start with 1, if that results in the OS indicating the port is not connected try 2, then 3, then 4 etc. Actually I would start with 4 if using USB to Serial conversion. From watching the Powerhome forum users have found that some USB to Serial converters are better with a Serial PLM than others. I do not use these so I cannot suggest a specific manufacturer.
A USB PLM does come with a USB cable. A Serial PLM is designed to connect to a Serial port so a USB cable would not help. Actually a USB PLM is a Serial PLM with a USB to Serial converter built in.
I don’t have a win7 64bit environment but I believe other users have indicated the OS has a means of displaying the com port number of the USB ports. Perhaps through the equivalent of the Device Manager.
Let me know the results of using com port 4 particularly and see if the OS indicates a Com number for the USB port in us.
EDIT: sorry, forgot to mention this. The Timeout error is the result of using a Com number 1,2,3,etc that is not connected to the PLM