I have a Raymarine E-80 chartplotter. It has a NEMA/GPS signal out (two wires) that I port to my laptop through a serial to USB converter to get my GPS position to my PC navigation program (Offshore Navagator). This has worked great for years. Starting maybe a year ago, sometimes when I connect, the GPS signal seems to cause the PC to go crazy. The pointer jumps around, windows open and close and move around on the screen, programs open. BUT NOT ALL THE TIME! Sometimes it seems to work just fine. I can tell that it related to the GPS signal because the serial to USB converter has a LED on it that shows the pulsing of the GPS signal and the action on the laptop corresponds. If I disconnect the USB plug, the problem stops immediately. The Raymarine manual lists a whole string of NEMA sentences that the output sends. Should some of them be turned off? It seems like if I start up the computer, then plug in the USB it helps but isn't 100%. Any other ideas what is causing this and how to remedy it consistently?