I can't import videos to my computer

I used to have no problem with this, just plug my phone in, open up the DCIM folder and copy my videos to my computer. But something changed in the past few days. Now when i import it it imports fine and it plays normally in windows media player. But if i use it for anything else the video just shows a green screen (there is still audio though). I found it odd that it won't even play in quicktime. I can't convert the video format either, it still shows up as green. Please help, i really need my videos on my computer!