My Minecraft worked fine months ago, but now it's glitching out all over the place. The title menu is cut in have and flashing, and the in-game environment is barely playable. I just downloaded the latest update. 

Intel(R) Core(TM) i3-3220 CPU @ 3.30GHz

6gb ram

My OpenGL version is 4.00

Windows 8.1 x64

All help is appreciated!