Many things can cause latency - the effects of latency are generally in audio drop outs and crackles and pops in audio processing. It can be caused by bad driver code, hardware, software like antivirus software, too small a buffer, not enough memory, a lack of separate audio interface, and probably some more.
Your system should have plenty of memory, but you do not list any type of audio interface. An audio interface is used for conversion of analog/digital and digital back to analog, and is also where things like mic/line inputs and outputs are located, for recording and playback.
By far, the best kind of drivers to use are ASIO drivers - and ones that will run in 64-bit mode are best.
Windows 7 x64 is a GREAT platform.
Can you list any audio interface you are using? Also, make sure if you are using one that Sonar is told to use the ASIO drivers, rather than WDM/KS ones.
If you do not have a separate audio interface, I would recommend you download and use a freeware product called ASIO4ALL. It should work fine in your system, and is a software ASIO driver that will give you good audio processing results on a system that does not have the advantages of a dedicated audio interface.
You can also locate and download another helpful piece of software called DPC Latency Check. There is no real installation - you just place the downloaded executable somewhere and create a shortcut to it. It gives you a scrolling display of detected latency on your system in real-time fashion. It will tell you if there are any latency isues - such as spike - that can interfere with audio processing. Upon detecting any such latency issues, you can then know you will have to go through a somewhat painful exercise of isolating the component or components that are causing the latency issues. Once isolated, you can either reconfigure, disable, or kick the dog as needed until things are running better. (No animals were harmed in the creation of this post - hee hee)
I hope the above helps,
Bob Bone