Hi friends
when I work on projects in any DAW (usually Sonar Platinum) and the size of vst's increase,  problems and noises and even sometimes tempo reduction occurs. Also sometimes I encounter to the error : Audio stopped .
Many times when I unplug my sound card my windows freezes and I have to reset.
Which part of hardware (or software) must I change? These are my PC info:

Motherboard: Asus H97-Pro
CPU: intel(R) Core i5-4440 - 3.10 GHz
Ram: 4 * 4 (16) GB DDR3 1600
GPU: Nvidia Gforce GT730
HDD: WD 1TB + 3 TB
Power: Green GP530
Sound Card: Line 6 UX2 [Buffer size: extra small 256 - 16 bit]
DAW: Sonar Platinum

Hi!
It's hard to say, in theory it must work fine.
Do you use freeze? It is hard to make big projects without it, even on powerful CPUs.
Anyway I strongly recommend you never use 16 bit, if you are not making final mp3.

I'd look at the settings on your interface and/or freezing your midi tracks.  Are your samples stored on the same drive as your projects?

dwardzala
Are your samples stored on the same drive as your projects?

No. My projects are in drive E (first HDD) and VSTs are in drive H (second HDD)

Edit:  Disregard my comment about your ram.  I misread your specs.  Doh!
 
Are either of your hard drives "green" drives?  These are not good for DAW use because of the power-saving features.

JonD
Are either of your hard drives "green" drives?  These are not good for DAW use because of the power-saving features.

My second HDD is purple but I don't know about first. I must open the case if it's necessary

Adq
Do you use freeze? It is hard to make big projects without it, even on powerful CPUs.
Anyway I strongly recommend you never use 16 bit, if you are not making final mp3.

I "Archive" the vsts after my project is completed and is ready to bounce. but while working they are active. I don't think my projects are so large! 

SevadaX6

JonD
Are either of your hard drives "green" drives?  These are not good for DAW use because of the power-saving features.

My second HDD is purple but I don't know about first. I must open the case if it's necessary

I don't mean the actual color of the drive.  By "green" I mean eco-friendly (with power-saving features), like your power supply.
 
And you don't need to open the case.  If you go to Device Manager - Disk Drives, your HDs will be listed by model.  You can then google them to see if  they're "green" or not.

JonD
 
 
I don't mean the actual color of the drive.  By "green" I mean eco-friendly (with power-saving features), like your power supply.
 
And you don't need to open the case.  If you go to Device Manager - Disk Drives, your HDs will be listed by model.  You can then google them to see if  they're "green" or not.

Thanks. So my first HDD is : WD Blue 1 TB 
and second is : WD Purple 3 TB

BTW, what is your operating system (Win 7, 8.1, 10)?