Firstly, ensure your copy of Windows is up to date with service packs, Microsoft updates, etc. Also ensure you have the latest sound card driver for your operating system from the manufacturer's website.
Next, run an sfc /scannow from the command line to check for any corruption in your Windows system files.
Failing this, grab a free copy of LatencyMon.
LatencyMon checks if a system running Windows is suitable for processing real time audio by measuring DPC and ISR excecution times as well as hard pagefaults. It will provide a comprehensible report and find the kernel modules and processes responsible for causing audio latencies which result in drop outs.
Taken from their website:
Windows is not a real time operating system. All requests to the operating system are delivered on a best effort basis. There are no guarantees whatsoever that requests are delivered within a certain time frame, which are the characteristics of a real-time operating system. That is not a problem for most devices and tasks but this is bad news for audio applications (which are considered soft real-time) because they need to deliver data to the subsystem and the hardware in buffers several times per second. If one or more buffers miss their deadlines and are not delivered in time it has audible consequences which are recognized as dropouts, clicks and pops.
There is a good article on the tool over on betanews too for extra reading.
