I've recently installed Kubuntu 12.04 on one of my desktop computers, dual-booted with Windows 7. Both operating systems were newly installed after I replaced the machine's motherboard and CPU. For the most part, all is going well; the only problem I've run into (so far) is that I'm getting no audio to the speakers. I've tried from both OSes. I've tried from Amarok, mplayer, Dragon Player, and Windows Media Player. I've tried web-based video, mp3 files, .mpg files, .wmv files, and DVDs. No sound to the speakers (or to headphones).

I've installed numerous different operating systems, including several Windows versions and several Linux distributions, on a variety of machines, and I'm comfortable using the Linux command-line, but I don't have any experience with audio issues. Heretofore, the audio has simply worked.

Any ideas where I should look for a solution?

Well, if you haven't already, the first palce I'd look if it doesn't work for anything is to see if it's turned off in a BIOS option.

If that's not the case, then run dmesg and look to see if the audio device is being picked up.

Further troubleshooting really would depend on that info. The fact that is doesn't work in any OS usually points to a BIOS or hardware problem. Lack of proper driver/modules comes in second.

could you give us the output for :
lspci -v
lsmod

NyteOwl, I re-booted and looked at the BIOS options, but I didn't see anything that looked like an option to turn audio on/off. I also ran dmesg (which is new to me) and got a huge output -- don't know what to look for in that.

MisterBark, I ran lspci -v and got another huge output, though not as big as from dmesg, and nicely sub-divided and labeled. Here's the output that's marked as related to audio:

(If you want the whole 152 lines, let me know and I'll post them.)

Running lsmod delivered 48 lines, as follows:

Please use code-tags, not quote tags for output of commands.
So, the kernel can see your sound hardware and has loaded the appropriate modules for the hardware. I assume that means that your hardware is working correctly.
Start alsamixer and look if all channels are unmuted. And the most obvious thing, make sure that your speakers are wired properly (this is often a cause for issues like yours)

Well... it definitely looks like you have not only the card connected to the pci bus, but also the driver loaded properly.

You don't have alsa?
What happens if you run "play /.../my-test-file.wav" ?

TobiSGD - Bingo! After installing the new motherboard, I had mis-wired the speakers. Thanks for pointing to the obvious! And thanks to NyteOwl and MisterBark, as well, for your ideas -- now I have a few more CLI tools to work with in the future.

You knew it since the beginning, that's why you've posted in the Hardware section.