You are not telling us what you already did and the results of that, so let's start guessing:
You need to check a few things.
First of all, check what communication mode is to be used.
The ADXL345 supports more than 1 mode.
You should try to use the same mode for both of your devices, and i'd suggest to use I2C (i'm not sure about the SD card supports that).
If you do use I2C, check what address is assigned to your device, each should have its own address.
And you need to check whether termination resistors are in use or not.
There should be termination resistors on 1 device only, prefereble the device that is farthest from your Arduino.
If you don't know the addresses and cannot find them in documentation, you can use Nick Gammon's I2C scanner.
That will tell you the addresses of any device that answeres its "ping".
And if you are mentioning "Your code", post it so someone can have a look at it.
Use the "insert code" button, to be found just on top of the text edit box you type a reply in.