Hello,
I have my device connected into my PC and I can access files and folder inside it through my PC.
I also have related drivers installed.
Still the “adb devices -1” shows
Usage: adb devices [-1]
I use Xperia U with ICS 4.0.4
you need to enable android developer tool and enable the debug function.
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Hi Thanks 
My phone drivers were not installed hence it was not recognizing the device.
Did it 