You need to contact the company via www.wmrecorder.com to request a refund.

It is really weird that the WM Capture worked fine in the trial mode and doesn't work for you in the full mode.

I don't really understand what "a lot of black screen during video playback" means. You can change the recorded area to avoid black strips around the video.

If you can't record video and get black/green/blue screen when recording, you need to disable video acceleration:
Black screen problem when recording video with Screen Capture software from Windows Media player