sims 3 there was an error during startup please see the log for more details

This is a frustrating issue, but I suggest that before you spend hours un-installing re-installing and messing around with your registry and such try clearing the game cache files first.

1) Go into your main boot drive and go into the Users folder - find the folder matching your account name and go in.

2) Once inside go into: Electronic Arts / The Sims 3 / DDCache

3) Delete missingdeps.idx

Then finally, cross your fingers, and try running the launcher after this.  Good luck!