big

This is a big glitch/bug or something else...Whem i start up my Minecraft it loads but the Main Menu is all in big pixels and letters too so i go into my world and some stuff seem fine (Frame Loading and Mobs...) but blocks look like theres some kind of space between them that i can see trough whole world not a block but whole world and my Steve (since i have downloaded version) suddenly brightens than turns dark like hes in some kind of dark shadow...than after few minutes of playing it crashes saying that its "Out Of Memory".If anybody knows a cause of this please send me a message with solution.

Thanks In Avance!