Hi

Are you referring to a midi keyboard or the 'keyboard in the software?

Either way they should work with the synthesizers - if it is a midi keyboard go through these tutorials by nihon69 to make sure nothing is wrong 

http://www.magix.info/uk/how-to-connect-keyboard-piano-with-computer-ii.online-training.130220.html

http://www.magix.info/uk/how-to-solve-latency-problem.online-training.130215.html

Have you downloaded and installed all the additional styles, synthesizers etc that are available - see under the Help menu for the Update program/Upgrade functions, Download free synthesizer ... option

John