Uploaded music does not play

In the last six weeks, most common behavior is that a song or two (or three) will play, then we stumble - the next song title comes up in the main window, the speaker icon appears next to it in the playlist or body, and the play button is still where it should be, but the progress bar is replaced by a blue gradient. No sound comes out (even when I leave the computer on overnight and it has six hours).

Seems to be limited to songs uploaded via iTunes Match - 'Matched' songs play fine.

Plays fine on 2 iPhones - limited to Windows PC. Same behavior on several networks (home, work, friend's house).

Have tried: reinstall, replacing library. Win 7 64-bit, itunes 12.1.1.4.