Have you tried this:
 
Start menu->right click on Computer->Properties->Advanced system settings->Advanced->Performace->Settings->Advanced
 
In the processor scheduling box, make sure Adjust for best performance of background services is checked. 
 
Don't know if it'll help your particular problem but it is a basic DAW optimization technique. 

@REZA
 
Quoting your response from above: "I bypassed the effects. Ok now it wouldn't hit the end and project wouldn't stop anymore but still the first core indicator shows more usage compare to the left 7 cores which are going up and down 1/3 of the first one.Any idea?"
 
It would seem to me that you have one or more effects that are causing your issues.  There are plugins that are specifically designed for use in Mixing and/or Mastering, and NOT intended to be used for tracking/recording.
 
Additional plugin issues include generally faulty plugins OR 32-bit plugins that do not play nicely with BitBridge in 64-bit Sonar.
 
I would suggest you avoid recording with plugins that are CPU intensive, or those that use look-ahead processing, AND I suggest you review the use of 32-bit plugins in a 64-bit Sonar installation, as SOME of these can cause problems.
 
Try going through your plugins one at a time, until you get it figured out.
 
Bob Bone

sharke
Have you tried this:
 
Start menu->right click on Computer->Properties->Advanced system settings->Advanced->Performace->Settings->Advanced
 
In the processor scheduling box, make sure Adjust for best performance of background services is checked. 
 
Don't know if it'll help your particular problem but it is a basic DAW optimization technique. 

thanks
I think i have done it before but i will check it.

sharke
Have you tried this:
 
Start menu->right click on Computer->Properties->Advanced system settings->Advanced->Performace->Settings->Advanced
 
In the processor scheduling box, make sure Adjust for best performance of background services is checked. 
 
Don't know if it'll help your particular problem but it is a basic DAW optimization technique. 

thanks
I think i have done it before but i will check it.

robert_e_bone
@REZA
 
Quoting your response from above: "I bypassed the effects. Ok now it wouldn't hit the end and project wouldn't stop anymore but still the first core indicator shows more usage compare to the left 7 cores which are going up and down 1/3 of the first one.Any idea?"
 
It would seem to me that you have one or more effects that are causing your issues.  There are plugins that are specifically designed for use in Mixing and/or Mastering, and NOT intended to be used for tracking/recording.
 
Additional plugin issues include generally faulty plugins OR 32-bit plugins that do not play nicely with BitBridge in 64-bit Sonar.
 
I would suggest you avoid recording with plugins that are CPU intensive, or those that use look-ahead processing, AND I suggest you review the use of 32-bit plugins in a 64-bit Sonar installation, as SOME of these can cause problems.
 
Try going through your plugins one at a time, until you get it figured out.
 
Bob Bone

Thanks Bob for replying
No I never use plugins for recording. I just use them for mixing.Also I do have the Mercury bundle which supports 64bit, and i should say i use sonar x1 32bit always because of some plugins which are not 64 bit. Also I should add something , some times during working every thing is fine but all of a sudden i hear a really really  loud white noise out of my speakers and sonar first cpu indicator hits the end and force me to close the program and reload it. 
 

robert_e_bone
@REZA
 
Quoting your response from above: "I bypassed the effects. Ok now it wouldn't hit the end and project wouldn't stop anymore but still the first core indicator shows more usage compare to the left 7 cores which are going up and down 1/3 of the first one.Any idea?"
 
It would seem to me that you have one or more effects that are causing your issues.  There are plugins that are specifically designed for use in Mixing and/or Mastering, and NOT intended to be used for tracking/recording.
 
Additional plugin issues include generally faulty plugins OR 32-bit plugins that do not play nicely with BitBridge in 64-bit Sonar.
 
I would suggest you avoid recording with plugins that are CPU intensive, or those that use look-ahead processing, AND I suggest you review the use of 32-bit plugins in a 64-bit Sonar installation, as SOME of these can cause problems.
 
Try going through your plugins one at a time, until you get it figured out.
 
Bob Bone

StarTekh

Hi Thanks for advise. Ya it was really helpful to run the rest of my cores.
 

I wish you had posted your system specs - I have been thinking you were running a 64-bit install of Sonar - my fault for not asking, I suppose.
 
Have you tried increasing your buffers?  This would be Preferences>Audio>Sync and Caching, try altering the Playback I/O Buffer Size from 250 to 500, and the same for the Record I/O Buffer Size (set to 500).
 
It should help you during mixing.
 
Bob Bone
 
 

There is also a parameter in the AUD.INI file that Sonar uses, called DropoutMsec, and it has a default value of 250.  You could try altering that to 500 as well.  Its value is in milliseconds, and is a time allotment used for Sonar to detect data starvation.
 
To edit it, go to Preferences>Audio>Configuration File, click on the Edit Config File button, make the change, save the text file, then click on Reload Config Settings to pull in the new values.
 
Bob Bone
 
 

robert_e_bone
There is also a parameter in the AUD.INI file that Sonar uses, called DropoutMsec, and it has a default value of 250.  You could try altering that to 500 as well.  Its value is in milliseconds, and is a time allotment used for Sonar to detect data starvation.
 
To edit it, go to Preferences>Audio>Configuration File, click on the Edit Config File button, make the change, save the text file, then click on Reload Config Settings to pull in the new values.
 
Bob Bone
 
 

Thanks Robert yes i changed them as you said. it is better now but i think i should play with is values for each song to get the best result. but i was checking youtube, i found out all the users have same problem i mean the first core indicator in sonar always is higher than the others, when the project is heavy and first indicator hit the end the other cores wouldn't help to make it even and prevent the drop out. they are always lower than the first one.
:)

I'm not seeing your OS - Window's 7?
If so,
Yup - you'll get that... Microsoft issue.

Supposedly Win 8 offers improved core balancing, so I'm watching other's posts of Win8/Sonar X2 with interest.

A work-a-round is to increase your buffers/latency on playback/mix, and disable FX with lower buffer/latency during record...
...you can also bypass select track FX to lower CPU load.

Good luck,
MG