This eliminates (for now) a possible video driver problem.

I would do:

1. Uninstall the aircraft and delete any remaining file
2. Disable anti-virus and firewall
3. Restart the computer with a/v and firewall disabled
4. Run FSX for a few minutes
5. Re-download the product
6. Reinstall
7. Reboot the computer
8. Run FSX and - I hope so - have 757 running correctly
9. Enable a/v and firewall

Regards

Schmid