I noticed when I came to Sonar that it appeared to be a little more susceptible to audio drop outs compared to the version of Cubase I had been using, it was managable as it only appeared to be happening when I was say copying to external drives or doing some other cpu intensive task and so by ensuring that my CPU wasnt overtaxed I was ok
 
I had to re-install my OS and Sonar is dropping audio even in situations that prior to the install would have been fine.
 
So not sure where to start to get this sorted

You'll need to supply a lot more information. Dropouts are normally easy to fix, but without having a clue about your system there's no where to start making suggestions. 
List your computer, OS and which audio interface your using. 
But normally dropouts are from interference from background processes. Buffer settings etc. 
Make sure you optimized your computer , run a DPCLAT test and so on. 
 

Yes, a re install on the surface seems like it might solve problems. But of course you may lose drivers and configs that got your system up to snuff the last time.
 
As JohnnyV says list you specs (like the data he does in his sig). That will help out those that can help you here.

Also a fresh install will probably enable have every device and service in the OS..."drop out" stuff you don't need to stop "drop outs."

A good IT shop keeps meticulous records of installs, updates and removals.
 
Each muso (even hobbyists) could benefit from that practice.

Yep - a lot more info needed if you want our full 2-cents. FWIW, the last time I did a full OS install; Sonar / other music software performance improved greatly! I consider up-to-date hardware drivers matching your OS to be part of a "full" system re-install. Also, some housekeeping with vst plugins and synths is also required from time to time. A poorly written plugin for "your" system can cause problems with DAW software.

I typed out a long reply but my computer crashed and since this forum is awful and doesn't offer auto-saved drafts this will have to be short.
 
Step 1: check Task Manager, make sure nothing is using too much CPU. Remove, fix, or upgrade anything that is.
Step 2: check DPC Latency Checker. If that goes into the red, your drivers are bad. Upgrade the drivers or disable the hardware - usually networking or external storage drivers. (Also, don't copy things to USB devices when you're doing something CPU intensive.)
Step 3: check Process Monitor. Warning - this is a complex tool and can make your computer run out of memory if you leave it running too long, apparently. But it will show you a log of all the accesses programs are making to the file system and the registry so it can indicate when something is working hard in the background (which you don't want).

bapu
A good IT shop keeps meticulous records of installs, updates and removals.
 
Each muso (even hobbyists) could benefit from that practice.

With Windows updates there is an update history so one can see what has been done over time.  If you also DL new drivers and versions of programs and keep them you have a built in history of what has been done on your system. 
 
 

I hope all my issues are so easily resolved !
 
I realised that my  O.S. install was so fresh that I hadn't even performed any kind of system update and everything is back to normal since I installed Windows 7 service pack 1 and then as a result of that reinstalled the service pack 1 version of the drivers for my MAudio 24/96 soundcard.
 
And here's me thinking that I was going to have to try and identify something that was causing the problem when i actuality it was something that was missing that was the issue 

Thats good to hear.