Minecraft- black screen on a mac?

I have the completely legit, bought version of Minecraft. It is updated to 1.7.5 and has been working perfectly up until now. I do not have mods but I have texture packs.
Here's what happens: when I open minecraft.app the launcher works without any problems. It opens the game. It displays the 'MOJANG' logo when opened as it normally does, but where it would normally open to the title screen, it turns my computer to a completely unresponsive, black screen. My mouse will move across this screen but I can't get off it in any way.
There are no error messages or crash reports in the.minecraft files. I haven't used any files other than texture packs and they are all in the correct folder.
I'm running Mac OS X version 10.5.8. My 'About This Mac' says:
Processor: 2.66 GHz Intel Core 2 Duo
Memory: 4 GB 1067 MHz DDR3
Startup Disc: Macintosh HD

I would really appreciate it if anyone could give me some info on how to fix this problem.

Try reinstalling, ill be watching this question

I don't know. Sorry my best advice is buy a PC, then install, if the problem occurs than I can help you. Till then all I can say is your running mine craft on a os that does spreadsheet, not gaming, or anything else for that matter