Hi
16x2 display with HD44780 Controller ?
Your schematics would help much while solving this issue. There aren't much to connect, just four wires:
VCC - 5V
GND - GND
SCL - SCL
SDA - SDA
Have you tried this one yet?
If you have soldered something, the bus address is something else than 0x27 which is default without soldering any of those A0, A1 or A2.. How you define how they're suppose to be ? It's up to you which address you would like to use, in others words if you have e.g. two I2C LCD modules in same bus, then you have to change another one's bus address..
In that example just change line 7 LiquidCrystal_I2C lcd(0x27,16,2); 0x27 what ever your module address is.
TommiP