I then installed fsx and pf3 on windows xp. I create a flight plan in fsx. I then use pfe to select flight plan. I then push the connect to fsx button. I get red and green flashing lights on the airplane graphic on the pf menu. When I then go into fsx I do not see pf3 connected. I do not get the acars message like I did in windows 10. I uninstalled both programs and reinstalled them.
Regarding your Windows XP machine, this can happen after a bad PF3 install. Try re-running the PF3 installer over the current installation (without uninstalling first), making sure antivirus software is off. Then try again loading a flight plan and connecting. Some users have had to repeat this a few times; others have had no trouble at all.