Siemens and Prosave comms problem

Hi all,

Some help if it's not to much bother please.

I am trying to backup a siemens OP-7-DP HMI using prosave V7.4.0.0

The problem I have is that I cannot select a valid com port within prosave to use for comms. My new fangled modern laptop doesn't have a com 3. I am looking to use a usb to serial converter with a serial comms cable but this will need to be connected to com port 4. Any ideas on how I can set this up?? A screen shot is attached

Scratch that last post.

Once I tried plugging into Com 4 and then started prosave com 4 became available.

You tell it's the end of a long day my brain is melting at the easiest of tasks.