Softwares from Market place refuse to download despite already paying.

Every time I try to download a software on the Market place, it doesn't download. It shows up as 'downloading' but the bar doesn't move at all. A few of the softwares I've left "downloading for a couple months now. This has happened with three softwares now and it's getting frustrating. I keep wasting my money just for a game not to download. Please fix this.