ieee1394 轉到電腦畫面變暗

That's usual, since the revolution and refresh rate are different in PC monitor and TV, so even if you use your pc to play a DVD movie, it is darker than you play in TV. so you need to set the contract /bright level in your PC monitor or on the software. I prefer to set it on software level, so that when you switch back to use the computer or other application, it is still using the previous setting.

what software you use to play back the moive after transfer to the windows?

e.g. Mediaplayer, you can adjust the contract and bright level.

P.S. I know some new monitor have the feature to auto-adjust the level, but don't know the preformance.