Clearing the proxy files removes all the files from the last time you cleared the proxy files. As soon as you start working on a production, the proxy files are immediately rebuilt for that production only (you got rid of the old crap).
Sorry but I have to ask, if you go to tools/options, is the program set to hardware or software rendering?. If it set to software, run the test. If it goes to hardware, then look at the pan and zoom. If it goes to software, again look at the preview screen. Do you see it in either hardware or software?
In either case, and if you haven't done it very recently, update the drivers for our video card.