To put it simple, I'm pretty fresh at the Arduino world, and was trying my way around with my Arduino Mega 2560 in this tutorial: http://arduino.cc/en/Tutorial/LiquidCrystal, and it came out just fine. I then implemented it on my project: A temperature-measuring circuit with a LM35DZ sensor, and it came out fine as well. I called it a day and powered off the circuit. When I powered up the circuit again, the 16x2 LCD just went wacky, showing up messed up characters, pixel blocks, or even nothing at all. I've tried everything: changing Arduino (a Duemilanove and an Uno), changing the board, jumpers and the LCD, and nothing helped. I even rolled back to the tutorial code, but it hasn't changed.