Hi i can see in piano roll that my midi keyboard is responding, but i cant hear anything?ive tried everything i can think of?Any ideas would be appreciated

You have given us absolutely no information,,,how can this be solved? 
Please supply more details. 
Tell us how you have it set up and what equipment your using to do this, what soft synth etc.
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It really helps a lot if you post your set up in your signature.  

Excuse my newness to this stuff, how do i add my details to my signature?...anyway im using windows 10, 64 bit, i have a presonus audiobox 1818 interface and im using the standar bass softsynth .and i have sonar platinum 2016.......what else do you need to know? 

To add a signature, click on "User Control Panel"  - top right, and then look to the left for "Signature and Comment"

As regards no sound.  Make sure the Windows 10 drivers are installed for the presonus audiobox 1818 interface. 

Then make sure they are selected in sonar (Preferences press (p) and look under Audio | devices and MIDI | devices)

First thing to do is insert a synth Menu item Insert | softsynth.  Make sure your soft synth is routed to one of those enabled audio devices.

Look in the Sonar help and look at "Tutorial 4 - Playing and recording software instruments" - under there you will find a section "Adding an instrument track to your project".  Hopefully that should get you started.

Do you have a midi track routed to an audio track (or a using a simple instrument track)?  Do you see meter activities on the audio track (or simple instrument track)
 
Is you audio track routed to a bus or main outs?
 
Do you have speakers or headphones connected to your interface
If you are not running sonar can you hear audio through your interface from another source (e.g. iTunes or YouTube)?
Do you have another audio  source running when running Sonar?
 
Sorry for the basic questions, but we have to start somewhere.

Yes thanx guys, along with customer support i figured it out....i think........Yes i had sound in general, my sound card was working, i had been working in sonar without my midi keyboard for a little while.......customer support suggested i set up my midi track via the new(i think its a new sonar feature?)add track feature.....where i just selected instrument and omni through add track...and i have sound..........i dont know why it didnt work the old way i used to do it........which was simply choosing omni in my output console outs?????