My computer does not let me download any files, it starts to download and then it just stops.

I recommend a download manager. This will help you keep track of what you've downloaded, where it is, etc. Best of all if something is causing your downloading to stop the software will try to pick up where the download left off. Free Download Manager - Free software downloads and software reviews - CNET Download.com

There could be several things causing the issue but I'd start with this and see what it tells your system just stops the download.