If the timer is stuck at 0:00, then the video file will be empty so that is why it won't open. We need to check why it was stuck at 0:00 though. Can you do the following please:
1 - Start FBX and go to the Support tab.
2 - Change the Log Level setting to 'Verbose'
3 - Try to record again
4 - When it gets stuck at 0:00, go to the Support tab and use the Send a Problem Report to send us your log files.
5 - Change the Log Level setting back to 'Normal'