I posted this on Ubuntu Forums and have had no replies, so I'm repeating it here:

This is a tickler. I installed a new Seagate 2Tb SSHD as a clone of my WD 2Tb HDD using Clonezilla. I made the SSHD the primary drive /dev/sda by swapping the SATA cables. As soon as I did so my speakers and webcam stopped working: pulseaudio said there was no sound card and cheese said there was no webcam. Thinking I had forgotten to disconnect the power cord when installing the new SSHD and had shorted the motherboard I was about to buy a new sound card. However, as a test, I reversed the boot order at the BIOS screen when booting up. To my surprise the webcam and speakers were working again.

Does anyone have any ideas as to the cause?

I had thought that the SSHD would be faster and more reliable as the primary, using the WD HDD as backup and secondary drive.

When you were running with your SSHD as the primary did you try using lspci / lsusb or check the dev directory to see if the kernel recognized them at all? Because if the kernel sees them but pulseaudio that would mean there is an issue somewhere between the kernel and pulseaudio. If the kernel does not see them check your logs for any errors or warning.

I think I did. I followed all the suggestions I found.

What puzzles me is that the SSHD should have had exactly the same kernel image as the HDD, after cloning the latter to the former with Clonezilla, and therefore behave exactly the same. Should I have reinstalled Ubuntu 15.04 on the SSHD in the Ubuntu partition?

Hmmm. One of my lines of thinking was perhaps your new sshd loads a new kernel module and that conflicts with the module for your sound card but honestly it is a pretty weak line. Everything else I could think of would require the kernel seeing the card while the sound server did not.

Is your Webcam integrated into your system or USB based.

You do not need to reinstall for a new hard drive or even clone the drive really as a backup / transfer could just be a tarball. I would just say on that subject do what is easiest.

My webcam is a Logitech C310 USB webcam, not integrated. My desktop is an HP Pavilion p7-1247c, 64 bit AMD. The sound card is IDT 92HD89E, which, by the way, Windows 10 is not supporting at the moment! (So, that's a plus for Linux).

lsusb:
Bus 005 Device 005: ID 046d:081b Logitech, Inc. Webcam C310

lspci:
00:14.2 Audio device: Advanced Micro Devices, Inc. [AMD] FCH Azalia Controller (rev 01)

I can continue to run with the SSHD as secondary (/dev/sdb) and just use it for backup, but the original point of getting it was the potential for faster access speeds and higher reliability.

The lsusb and lspci were on the WD HDD primary. I will run the same commands when I get a chance to reboot with the SSHD as primary.

After booting the SSHD, lsusb shows no webcam and lspci shows no audio. Furthermore the display is wide default format 1400x1050 with no other options selectable.

uname -a:
Linux civet 3.19.0-28-generic #30-Ubuntu SMP Mon Aug 31 15:52:51 UTC 2015 x86_64 x86_64 x86_64 GNU/Linux

Something weird occurred. When I swapped the SATA cables back and rebooted with the WD HDD as primary, the video and sound did not work, although the lspci and lsusb showed them present. I had to boot into Advanced Options/Upstart. This makes me wonder if I could get the SSHD to work if I chose another kernel. Stay tuned.

uname -a of the primary:

Linux civet 3.19.0-28-generic #30-Ubuntu SMP Mon Aug 31 15:52:51 UTC 2015 x86_64 x86_64 x86_64 GNU/Linux

which is the same.

Well, that was a blowout. None of the grub entries I tried with the SSHD provided working sound and video, although, it seemed, all of them showed audio with lspci and video with lsusb.