no sound, although made all connections

1. add a new qtractor/midi track;
2. connect your midi keyboard to qtractor/midi master in.;
3. connect qtractor/midi master out to qsynth midi in;
4. arm the midi track for recording (track button [R]);
5. play on midi keyboard; check activity on qtractor/mixer midi track and then via master out to qsynth;
6. set record ready (main red circle button);
7. hit play (main blue triangle button): recording starts;
8. play your part on the midi keyboard; check that notes are draw on midi track (growing red shaded region);
9. hit play again or stop when satisfied; rewind;
10. hit play; playback starts; you should hear your part on qsynth;

which of the above steps doesn't work as you say?

cheers

re. don't know how I can "check activity on qtractor/mixer midi track and then via master out to qsynth"
open up the mixer window (menu View/Windows/Mixer or press F9) and watch for any change on midi master and track strip meters. if you don't see it it's because there's no midi flow coming in or through.

please note that midi channel must match to midi track's one. also, check whether monitor is set for the track (track/auto-monitor might come in handy here).

cheers