You said that you put SL on your exceptions list but make sure its set as a trusted site.
There is something you might try but 1st when you reinstalled SL did you uninstall it 1st if not you simply replaced damaged files without changing anything.
If you reinstalled (using the same location) w/o uninstalling then try this;
1.) On the login page click edit
2.) Click preferences
3.) In the network tab, click the button that says "clear cache"
4.) Under the web tab, click the "clear now" button next to the browser cache
5.) Hit OK then close the program and restart it
If you reinstalled the program w/o removing the cache files (and I'm not sure uninstall would necessarily remove them to begin with) what you told me sounds like the kind of problems I have had.
When you ctrl,alt+del the program, it didn't shut down properly which clears the cache (A.K.A. stored memory) and every time you try to log in, the full cache can't hold the data needed to complete the connection.
I hope it helps you. I know it’s worked for me for numerous problems including inventory that seemed to go astray.
BTW besides physical cleaning your comp & running your antivirus there is another cleaning you can do. That is cleaning your hard drive of old internet & temp files that take up memory allocated to processor use.
I use ccleaner (you can get it here http://www.ccleaner.com/) I recommend that you only use the cleaner, the registry cleaner may take out things you need if you don't know what the look for.