My sims 3 game launcher wont open

Hi.

Ok, so I put in my Sims 3 as I usually do, but the game launcher wont start. It pops up but a sign comes up saying "There was an error during start up. Please see the Log for details."
I have no clue what or where the "Log" is and I don't know why it's doing this now.

Pleeeease help!!!!