No sound (mechanical): can I buy a new audio jack socket & stick it in a PC?

I've no sound on my work computer which looks like it's probably one of these: "Windows 7, Dell Optiplex GX620 Desktop PC, P4 HT 2.8GHz, 1GB Ram, 80GB Hard Drive, DVD".

Apart from the mild annoyance of not being able to listen to YouTube playlists as I work, I also can't listen to all sorts of useful work-related audio or audiovisual clips - Prof Harold Thimbleby (in video below) is the Swansea PI on the CHI+MED project I work on. He's talking in London tonight and I thought I'd have one of his earlier talks on in the background.



If I turn the volume and hold my foot against the headphone jack I can hear things OK, through the left headphone. Moving my foot at all means sudden silence, and the unit (which also houses a speaker) is clearly a bit wobbly.

I'd previously checked the sound settings and used the little troubleshooting programme from Microsoft (available from that link once you've gone through the first bits) which found no problem. It's definitely mechanical.

How easy is it to
a) get a new unit
b)i) plug it in
b)ii) and what safety things to I need to be aware of? For example I'm wary of poking around in the back of a television (mine's CRT) because I understand there are fearsome capacitors within it so even with unplugging it there's still a high voltage... might be wrong, but if I unplug my PC do I need to wait hours / weeks before unscrewing things?
c) is it likelier that I can fix this by just opening it up and resoldering it, in which case I'd still need an answer to b)ii ;)

Ta :)

Honestly for the last year every time I've wanted to watch / listen to a YouTube video I've either emailed the link to myself and picked it up on my iPhone, or used an URL shortener to then type a short URL into iPhone Safari, which then automatically loads the YouTube app. There's always a workaround but it would be a nice sense of achievement to fix this!