I'm seeing a lot of people with this problem, it has even happened to me. Don't worry it's very easy to fix.
It appears Rockstar is tampering with something ( my guess is they are trying to fix the online servers ) and while doing so created another problem that is affecting a large majority of players. (And yes this issue is effecting people who only want to get on to play single player)
The solution to this problem is rather simple DO NOT DELETE YOUR GAME SAVE FILES/DATA UTILITY FOLDER. The last thing you want to happen is lose your 20+ hour game play data due to this issue.
Now all you gotta do to get the game to load up properly again is just SIGN OUT of the PSN and restart the game WHILE DISCONNECTED from the PSN and it will load up fine. It's as simple as that. If you still can't load up and it just stays at the loading screen forever try turning off the Information Board on your PS3 and starting the game while disconnected from the PSN.
And no i'm not talking about the freezing issue while in game your screen freezes and completely stops. I'm talking about this very recent issue that just started happening where the game wont start for many people and just sits at the loading screen forever trying to start from where you last left off.
Sorry if there is allready another topic covering this issue but it is very recent and ive allready read about people deleting their files and i feel bad for them =/