I'm using SAI on Windows 7 - 64 bit on both my laptop and my desktop (for about 6 months now). I have experienced no problems of that nature (in fact, this is one of the most trouble-free applications I've ever used!).
Taking Win7 down is pretty hard for any application. If you have a registry-repair application, you could try that.
Where is your SAI installed on your system (Program Folder or a folder in your local profile?). If it's not local, try moving or reinstalling it to your documents or picture folder. Or try downloading a fresh copy and install it somewhere else (and move your licence file over too). Maybe one of the files in your old install has become corrupted.
Do you have the latest drivers for your video card? What kind of hardware are you using (processor, Ram installed, etc..). Installed anything new lately (hardware or software)?