I'm guessing there are some gamers here.  GTA5 for the PC didn't seem to start for many people.  I personally spent hours looking for a solution; as none of the online solutions/suggestions worked.  I figured maybe this forum post may be helpful to some people.

I was able to resolve the issue by curing all three of the items below.  It's the first PC game I had to literally jump through hoops to get it working:

1.  Updated GTAVLauncher.exe (official pre-release version).  I confirmed it's digitially signed by the same developer who created the original EXE.  Oddly, Rockstar isn't distributing this yet.  You can find it in the below blog post.

http://www.incgamers.com/2015/04/gta-5-crash-and-launch-issues-there-are-workarounds

2. Use Window username that does NOT have spaces or non-alphanumeric characters.  This was a PITA; having to create a completely new user profile; migrating all my profile data over. 

3.  And, finally... you MUST disable GTAVLauncher.exe from being skinned by Windowblinds.  This took me the longest to figure out; since there's no information about this that I could find anywhere.

Some laptop users with Nvidia graphics cards are able to temporarily disable their Nvidia display driver; until the launcher starts the game (reverting to your PC's integrated video card, if enabled), then re-enable the NVidia display adapter.  However, Nvidia SLI users (like me) may not able to do this; especially, if their Integrated graphics adapter is disabled already.