1) Delete everything to do with Second Life.
2) Go here and download second life again, http://secondlife.com//downloads/index.php
3) Run second life and the download thing will pop up for the last time.
4) Update the game for the last time.

5) After the update go back to second life, and its under maint. Meaning they are currently fixing the problem.
I have no idea how long it will take. I heard about 5 hours
.. But I dont think it will take that long.