Why can't i go into creative mode on Minecraft anymore?

I used to be able to play MineCraft on Creative mode on my computer but i can't anymore. I'm not online I'm just playing single player and I could only play survival, Even if i make a new world and start it on creative it will not allow me to play creative mode.

I also tried to type it in with "T" but when i press "T" it will not pop up the open chat menu, i checked in my options to see if someone changed the command but my settings tell me that "T" is the right command for Open Chat.

I'm playing on vanilla i Can't find out what's wrong!

I feel like It might have something to do with me downloading "Technic Platform" I can play Creative mode on that but I can't chat. My little brother did download a bunch of mods/game modes from the Technic Platform, but i still wouldn't even know how to fix that!

A link to the Technic Platform thing i'm talking about, maybe it will help find the answer i'm looking for!

Thanks for reading Please Help!

>><<http://technicpack.net/<<

Check that cheat mode is enabled for the world you're using.

If that's cheat mode is disabled, you won't be allowed to use commands.

Install Minecraft from minecraft.net instead of running it from Technic Launcher, make sure you are running the current version of Minecraft (1.7) and if that doesn't work, uninstall and reinstall Technic Launcher.

@Agent, even if cheat mode weren't enabled, he would still be able to type, but commands wouldn't work.