Go Start>Search
In search field put:
*.mp3
(make sure, you are searching your entire C drive)
All mp3 files will be displayed. Left click on first file, push SHIFT, hold it, and left click on last file. All files will be selected (highlighted). Release SHIFT.
Right click on any of those files, and click Copy (or Cut, if you don't want to leave files in old location), then in Windows Explorer navigate to directory where you want to put those files.
Right click on directory name, and click Paste.
Done.