Blank logon screen with cursor after svchost crashed

I was playing music with Windows Music player. Suddenly there was no sound, so I checked speaker icon in the tray bar, since I assigned one of my mouse button as a mute button and I might have accidentally clicked it. The speaker icon was not muted, so I clicked on it; instead of opening the volume bar, the cursor just showed a busy sign. After 3 to 4 seconds, the cursor froze. In another 3 - 4...