Shisa

I have used a combination of video clips and still images (.jpg) with transitions and two audio tracks (a narration and a BGM) to create a video. However, during export (which I can only do in AVI and WMW format, since I'm trying out the free/home version), the resulting WMW video showed no video at all, just the audio tracks played. In AVI, some of the images and transitions were shown, while during others black/blank screen was shown. Some cases, if an image is supposed to be visible for say 10 sec, screen is blank for the first 8 seconds, and then suddenly at the end that image will pop up. This was happening in video preview as well, though not initially. This only started happening in preview after I'd been working on the project for a couple hours. Tried closing the program, opening again. Tried exporting multiple times. Not sure why this is happening and what I can do to correct this. Any help would be appreciated, thanks in advance!