No audio device is installed

several months ago in an attempt to speed up my dated dell inspiron 1520 (vista), I uninstalled a series of programs - including a few I didn't recognize and/or didn't deem necessary - from the programs and features list. I think I somehow inadvertently uninstalled my audio driver from this location and as a result, I have not had sound on my computer despite my best efforts to disable, reenable, uninstall, and reinstall various drivers countless times. I still get a little red X over my speaker icon, even though my computer acknowledges that I have an audio driver installed (sigmatel high definition audio codec) and up-to-date, and it refuses to enable audio. my volume mixer simply states that there is no audio device installed. what could be the problem? do I need to do a clean reinstall of my OS at this point? I don't recall any service packs or updates interfering or being updated around this time, and I don't have system restore enabled as it was absorbing a substantial portion of space back when I did use my laptop regularly (I simply neglected to reenable it after I unloaded the rest of my programs; I'd never needed to use it before). it's really getting to be quite frustrating at this point as I've expended a lot of time and energy trying to fix the issue! thanks in advance for your help.