A problem that manifests itself like you are describing, has never been reported by anyone. No error message ? Just screen flashing ?
- Do you have FS9.1 installed ?
- Can you try downloading the Stand-Alone Addon Manager (which is the same that gets installed with all the sceneries, anyway, but it might repair things) ?
- What other modules you have installed ? Perhaps there's a new module out there we never heard of, that is not compatible with ours