Unable to download properly.

I’ve tried downloading to my laptop (vista) every couple of weeks since November, and the same thing happens each time - the DL cancels itself almost as soon as it starts. I get an icon on my desktop, but as the download is incomplete it is useless. I have tried restarting the download, but as soon as it’s complete the icon disappears and there is no evidence of the download anywhere on my computer.

The download worked perfectly on my mother’s XP PC.

Nothing I have done so far seems to have worked - even temporarily disabling Avast during the dowload. In my desperating I even tried using IE instead fo my usual Firefox in case that was the problem, to no avail. I’m beginning to despair. Help, please?

Don’t know why that’s happening, but if you have it on your mother’s XP machine why not copy it to a USB disk, external drive or burn a CD?