Saving windows movie maker video as a movie file wont work ? PLEASE HELP?

kso , this is a huge problem for me , because i made this awesome video which i want to get to youtube. i edited it on windows movie maker , and its 3:20 long. so its a pretty big file for my computer. when i go to save it as a movie file , a message comes up saying that it cant be saved , and theres something about disk space . so i tried everything , i did a bunch of disk cleanups , ive deleted unused files on my computer , i tried everything possible. even if i try to change the settings or whatever , the same message comes up every time ... can someone help , because i worked for like 3 weeks on this video and i want it up on my channel ?