I think i solved my problem..
Like i said in my previous post, now i am powering 74HC4050 through 3.3V regulator. I also added 0,1uF ceramic caps between VCC and GND of ATmega328, 74HC4050, 74HC595 and LCD.
Up till now (after half an hour of testing) everything works fine, without problems.. And i hope it will stay that way 
Thank you for all guys! 