I have a Dell Inspiron 1525, and sound problems have been very common. In Windows XP the OS used to frequently stop detecting the Intel HDA, and I used to get no devices found errors. After installing ubuntu, I did not get it for a couple of years. Until today.
Check whether you're getting sound with windows, if you dual boot. This is why you should dual boot, it gives you idea about hardware and software problems. In my case, to start off, sound was not working in windows too.
So I run the boot-diagnostics. This is by pressing Fn-power instead of power, or choosing diagnostics from the boot options menu by pressing F12.
I notice that the standard thing that used to come up is gone. Weird. Now I get loads of memory checks, with no sound check options. Anyway, after the checks, I restart windows, and sound works!
I download the diagnostics software from the dell website. This is priceless. I run this, and it does detect the sound, as always. It's just not running in Ubuntu.
Turns out it was an ALSA issue. All I needed to do was reinstall the alsa files. Run this, in fact -
sudo add-apt-repository ppa:ricotz/unstable; sudo apt-get update; sudo apt-get --reinstall install alsa-base alsa-utils; killall pulseaudio; rm -r ~/.pulse*
However, this is for maverick, and so please check this website -
https://help.ubuntu.com/community/SoundTroubleshootingProcedure
Sound is back now!