What is the type and specks of your PC - windows ? if so what version ?
Are you intention to use this PC only for
navigation ?? or multi use ??
Your problem seems at first look to be a poor /& vrong vga driver but difficult to know for sure.
Would recommend to try to download the latest
Opencpn for your operating system from
Download OpenCPN | Official OpenCPN Homepage
and try to start
opencpn after installing. If windows, go to system-> decivemanager with your
GPS plugged in. Look for crratd COM port and note the higest number, normally COM3. Go to opencpn menu/settings and choose connections. Add a new connection and chose
serial. and mostly you will see your GPS as COM3. press apply and check "show
NMEA debug Window. Do you see the
NMEA stream with green letters in that window ?? Then everything is just fine. The latest opencpn has chart downloader included in the install so you can download all official nooah
charts using the chart downloader. Be sure to enable the chart downloader in the plugins menu before going to charts->chart downloader.