Replying to Mac trouble for exporting clips fcpx

So I have had fcpx for about two years and all of a this last month the export does not work. It says share failed. I don't know why the video exports in MPEG4. Does anyone use fcpx and has this same problem. How do you export to the .mov or mp4? Also sometimes like 4 minutes after the video export fails it shows up in QuickTime but it has lag and is shorter than the actual video.

Please help I cannot export my video at all

+k for help

Ps I have the latest version of Final Cut Pro I have a Mac book air with Yosemite if that helps at all

Thanks

Marcus