No data in Tables after installation

Hello friends,

In our company , we have installed a new SAP R/3 4.7EE.

Installation went on well.

Now i want to work extractions from this R/3 system to BW. But i neither find data in Tables like Mara, Marc etc nor in the data sources.

How can fill these tables/datasources with data so that i can work with extractions.

Please let me know how to proceed in this case.

All your suggestions are welcome.