RTC and accelerometer data issue

Hello, I am trying to retrieve data from an RTC module (DS3231) and an accelerometer (GY-521) on an Arduino Uno simultaneously. However, when both SCL/SDA cables are connected only the RTC will output data and the accelerometer will only spew out 0s. They both work fine when connected on their own. I am new to Arduino and all this world and I'm having problems understanding the information available. Basically, at this stage, I think my problem is with the actual setup (not the code at the moment). Could someone advise me on the correct form to connect these two to the Uno? Many thanks!

You have two slave I2C devices that are operating at different voltage levels. It depends very much on the actual breakout board if that can work without modification but your post is unfortunately missing the necessary links to the exact products you use. Provide the necessary information as the sticky post at the top of the topic instructs you.