I2C bus not working at all

Hello. I am trying to read registers of MPU9150 using Arduino Uno via I2C bus. The code uses Wire library which comes preinstalled with Arduino IDE(I am a newbie so sorry if you feel it is obvious that you know it). I am using A4 as SDA and A5 as SCl. When I check the voltage of SCL and SDA pins on oscilloscope, I get a constant voltage of 4V on both the pins which should not be the case. I should get pulse waveform atleast on SCL pin.
So what is going wrong? This is my third day to get this working but it is still not happening.

Run the i2c_scanner : http://playground.arduino.cc/Main/I2cScanner
It should find the sensor. When it can't find anything, something is wrong with the I2C bus.

Does your MPU-9150 module has a voltage regulator on the module ? If you are sure there is, you can power the module with 5V.

There are Arduino Uno boards (cheap clones and copies) that have the I2C not connected. There some posts about it on this forum. You could try to measure if the A4-pin and SDA-pin are connected to the ATmega chip, and also for A5 and SCL.

Are you using pull up resistors to Vcc on both I2c lines? Are you using the Wire library correctly? (Wire.begin(); etc...)