Which "IMU" and what interface are you using (SPI or I2C)?
It matters because some IMUs 'support' both interfaces but, to keep the device from detecting the wrong interface certain signal lines (probably clock and CS) must be held at certain levels at power up. I don't remember the specifics, but it is important and usually solved by adding a pullup resistor or two.
Net: Check the datasheet for the IMU and see what the requirements are and make sure they are met.