When I load Addictive drums or EZ drummer + several vsts - starts cutting the tone, 
 
I use 1 track for drums 
1 track for guitars on which i use ts808 vst then le 456 engl emulator then poulin lecab 2 add  4 different guitar impulses one eq and reverb and its okay but if i duplicate the track all hell breaks loose .
 
Intel Core 2 Duo P8400 (2.26GHz) 6 gb ram ddr 3 win 7 asio drivers for lexicon lambda external audiointerface.
Intel graphics card HD 8500 or 8700 not sure any advise ?
 
As you know for recording metal i need at least 6 tracks 4 guitars 1 bass 1 drums and 2 vocals .. this is the minimum. If it goes so bad on 3 tracks what do we make of 6 ... please advice me what to do ... im thinking of chaging the pc, but this one must be covering the requirements however this looks simillar to when u wanna play a game that minimum requirements are those and u have them but lets say the game for instance is real time strategy and there is a big battle the videocard and pc are not handling it too good ... does the same principle applies here ? or does it have to do something with my audio drivers

As you know for recording metal i need at least 6 tracks 4 guitars 1 bass 1 drums and 2 vocals .. this is the minimum. If it goes so bad on 3 tracks what do we make of 6 ... please advice me what to do ... im thinking of chaging the pc, but this one must be covering the requirements however this looks simillar to when u wanna play a game that minimum requirements are those and u have them but lets say the game for instance is real time strategy and there is a big battle the videocard and pc are not handling it too good ... does the same principle applies here ? or does it have to do something with my audio drivers.

It sounds like you're taxing your CPU. Are your meters high when this happens? Is there any difference if you increase the buffer size/latency?.

when i open task manager says cpu usage 60 70 percent and above, i think there is a difference because i first tried switching on 64 bits but sounded kind of latenced very slim barely noticeble but after returning to 24 it went ok but still the other issue persists

Extreme low latency settings will always tax your system more. It really sounds simply as if you're running into the limits of your computer/CPU. The combination of things you're doing (expecting super low latency, using lots of VST FX per track) is designed to make it difficult for your CPU.

I would suggest, if it's possibly for you, to increase the buffer size/latency and see if that helps. You may have to use some form of direct monitoring to hear yourself during recording though, because playing with a lot of latency isn't very nice.

I dont think it will help ... if it is simply cpu problem ( as far as i see it ) thats the most reasonable case, i need a new pc :) i guess 

OR i could use another more stable daw - for instance reaper but ... i already have sonar x 3 producer and i dont want to change it for something else ... 

60-70 % CPU usage tells it all, IMO. That high consumption practically always causes dropouts and such. Amp sims can be especially CPU hungry.
You need to plan your tracking workflow so that you can freeze tracks or disable some VSTs when recording new tracks.
 
What you say about 64/24 bits is a little confusing. Your OS and the version of SONAR are 64 bit versions, I assume (?). That is a totally different thing than recording using 16 bit or 24 bit setting. 24 bits is recommendable, and that is not resourcewise a crucial point compared to recording in 16 bits . SONAR handles everything internally in 32 bits as default, IIRC.
Or are you talking about the 64 bit double precision setting in SONAR?

So in other words i need to boost my CPU speed somehow or get a new machine ... because disabling and enabling tracks ill loose where I'm at or what am I singing/playing nd stuff

Before you go throwing money away, take some time and try and find out exactly what the problem is, thne you can formulate a plan for solving it.
 
What are your buffer settings?
What driver are you using, and have you updated it recently?
What is the reported round trip latency?
What happens if you bypass all of your Fx plugs (hit 'E'). If it's ok when doing this then all you need to do is a bit of pre-planning.
Get all you tracking done & finished before inserting any Fx plugs at the lowest latency you can mange. Then you can jack your latency up when mixing because at that stage, it really doesn't matter if your latency is 2ms or 200ms