Playback does not work (and MuseScore prevents computer from playing sounds in other programs)

• Dec 13, 2009 - 01:46
Graphical (UI)
S2 - Critical

When I hit the play button, nothing happens. If I hit space (which according to the manual ought to start playback) I go back into note entry mode, even when note entry mode was turned off.
If I go to Display > Play Panel, I can check the checkbox, but no Play Panel comes up. All other panels work.

I tested the sound using Rhythmbox (mp3 player). If MuseScore is open and I try to play something on Rhythmbox, nothing happens. If I close the MuseScore window, the song starts to play in Rhythmbox. If Rhythmbox is playing and I start MuseScore, Rhythmbox stops playing.

Ubuntu 9.10 (Karmic Koala) running on an IBM Thinkpad T60
lshw output for audio:
description: Audio device
product: 82801G (ICH7 Family) High Definition Audio Controller
vendor: Intel Corporation
physical id: 1b
bus info: pci@0000:00:1b.0
version: 02
width: 64 bits
clock: 33MHz
capabilities: pm msi pciexpress bus_master cap_list
configuration: driver=HDA Intel latency=0
resources: irq:17 memory:ee240000-ee243fff

Thanks for any help you can provide.