This might be cause by excessive thrashing This is when the disk becomes extremely slow becuase it is taking too much resources to keep the application alive and it is not contributing anything. Please see the wiki link below.
other applications running and not doing anything can cause thrashing. Specially after not being messed with for an extended period of time.
WMP11 has alot of what's called I/O reads. This is normal becuase as of right now my I/O reads for WMP11 are:
I/O Reads:612,003,098 (wmp has been open for 4 days)
commit charge (paging file usage):167,658K
RAM Usage:9,478K (working set)
this is kinda like packets transferred. I have one playlist file with 55 hours of music on the "list pane" and another playlist in the library main view that is 6 hours long. WMP has been open since 4 days ago. I normally have it reside as miniplayer mode on the taskbar.
Please see this wiki article on Thrashing becuase this is a very common problem.http://en.wikipedia.org/wiki/Thrash_(computer_science
I have an article here called "windows system resource manager".... Search for that and then you can find out how to keep the commit charge for programs trimmed to prevent thrashing!
Hope that helps!