Hi, when I wanted the AI players to have vehicle modifications, I was loading something, but the game crashed (because of some vehicles), so I had to restart my computer.
There was a known bug that caused LFS to hang when generating AI paths for certain mods that were created incorrectly (with "Max up" wrongly set). The bug was fixed in Test Patch D45.
I don't know why a computer would need restarting. In the case of a hang, you can "End task" or "End process" using Windows Task Manager (CTRL+SHIFT+ESCAPE).