Games won't download or install

I frequently download game trials that run for an hour - sometimes I buy them. I never had any problem doing this, except that some games needed a better graphics card than I had, no biggie.

Suddenly none of these games, whether I buy them or not, will download or install. Here's what happens:

I find a game, sometimes Comcast Chill, sometimes BigFish Games. I click on download, the file window opens that shows the little papers flying from one file to another. Suddenly the papers will stop flying and the window closes. Then nothing happens.

When the download window is open, it says it is being saved to TEMP files, but I can't find it anywhere, even if I use <search> to find it. I can find the TEMP files but they are always empty.

I'm using VISTA on a laptop. This is the computer I've always used to do this. I tried emailing both companies tech support but I'm not getting any answers.

Any suggestions?
Thanks!