I have recently inherited responsibility for my organization's website which was requisitioned outside of our IT department, designed by an external consultant and implemented on DNN.  Due to some performance issues responsibility for the website/server have been given back to the IT department (me) to figure out what is wrong with the site when, unfortunately, I don't have any experience with DNN.

What is happening is that numerous times through the day the server goes through periods of high CPU and Disk usage.  These periods of time can be anywhere from 2-15 minutes where these activities spike at 100% utilization.  At first these spikes seemed to correspond with whenever someone on the web development team added or removed a page from the website.  This makes some sense where DNN would need to then recompile itself.  What eventually started happening is that these spikes would start occurring when they claimed that no changes were being made to the website.  

Now I am tasked with finding the cause and resolution to this issue because during these periods of high utilization, the website is completely inaccessible.  So I'm looking for any suggestions, logs, tweaks, etc... that will help to optimize this server.  As I mentioned, I just had this fall into my lap and I don't have any experience with DNN, so please bear with me and provide details, I won't necessarily understand terminology and jargon related to DNN at this time.  Thanks!