You can get a blank screen if no player is installed or if the installed version is below the SWF version (trying to open Flash 5 with Flash 4 player). You may also have a malformed HTML wrapper for the SWF.
If the player is installed, try out FlashAssist. It lets you open SWF's directly without the need for a companion HTML file (which you need with IE). Also, it checks for which version of Flash player is installed and let's you know.
If you're sure you installed the player and FlashAssist still complains, your registry is somehow messed up. Hard reset or send me an email and I'll tell you what stuff to remove from the registry before trying another install.
You can get FlashAssist at:
http://www.antmobile.com
It's shareware but it's a fully functional eval version.