Where did you buy this computer? Is it new, or did someone else have it first?
I see nothing in WMP to start it automatically, and mine does not start at boot. So you must have something opening it to complete a task, or you system is corrupted.
I do not know if there is a task you can schedule in Task Scheduler, but you might check that.
There is an option to look for updates on a daily basis, maybe it is doing that.
Nothing in the Startup folder?
If it is trying to update your library, let it finish or put something in one for it to find.
Operating System Win 7 x64
Computer Type Homebuilt
OS Service Pack 2
DirectX Version 11
CPU Type and Speed i7 3770K
Motherboard Chipset Asus P8Z77-V Pro
System Memory Type 16 GB Kingston
Video Card Type and Speed Nvidia GTX 680 (2)
Computer Monitor LG 27" (3)
Hard Drive Kingston 240 SSD
Optical Drives LG WH12LS30 Blu-
Modem-Router Type Linksys E3000
Network Adapter Intel Gigabit
Anti-virus Software MSE
Computer Skill Level Average Ability
Windows Experience Index 7.7