Blimey, that's almost impossible to answer remotely...

There's any number of settings that could be off, and one of the problems is that something somewhere could be set to process the sound and deliver what you are hearing. Assuming the card itself is not indeed at fault, then the only thing to be done is open up every option and play with it, to see if it has an effect.

You mention upgrading to Media Player 8, but 8 is ancient (I think) - as I recall the last version that was pre-XP was version 10, and the current version is 11 for later systems, so allowing, or making the appropriate upgrade to the newest usable would be a good idea. If I'm right about 8 being so old, then it could easily be the source of the problem. Get 10 if the PC is not brand new, or 11 if it is. The installer should check the PC anyway, and tell you what can and can't be installed and run - I kept 10 for ages, and eventually got fed up being told to put 11 in, and eventually gave in.

There may be an issue with the sound card drivers, which can suddenly be rendered useless due to a change inside a Windows upgrade. Checking the drivers side of the card manufacturer's web site would be a good idea. Worth doing anyway.

I don't use Windows Media Player as a rule (it has to be used inside Windows, so can't be completely avoided), so am never up to speed with it, but those are the versions the last time I had to play with it.

I use Winamp for all my audio and video playback outside Windows demands, which come from winamp.com and could be downloaded and run as a check. Using it would confirm whether or not the problem is in the software or the card. If the sound with Winamp is ok, then the card is ok.

There is a slightly more obscure check you could try...

I've been using a program called Breakaway for a while, and been really impressed by it. I only ditched it recently because after a month's free use, it starts to deactivate itself after 30 minute's use, and I got fed up (and I'm not buying it).

It can be downloaded from http://www.claessonedwards.com/winmore.htm and I'd give it a try in this case because it replaces all the software drivers for the PC's sound system with its own software. Installing this and seeing how things sound would tell you if there was a problem with the software driving the sound card. Breakaway can just be uninstalled once the test was done, and your back to normal.

If you hadn't added that the change coincided with the "upgrade" I would have warned that most cheap PC speakers, even expensive cheap speakers (I bought a set of Philips powered cheap speakers - and they were vile) can sound bloody awful, and slapping a pair of real speakers from a proper hi-fi, stereo system, or whatever, is worth the effort for a quick comparison.

Keep us posted

What happens with earphones?  Borrow a headset. That should tell you if it is the speakers.

The moral of this saga might be - If you want good music get a hifi!

Use Winamp, beats Media Player for usability and can be integrated into Firefox with FoxyTunes (though I suppose it works with IE and other media players too.

Winamp gives you access to Shoutcast radio, and internet TV too, so you can get endless tracks of whatever music genre you prefer, all for free and legit (if you care).

You're stuck with Media Player (or Real Player) if using digital radio like the BBC, but you can use Real Alternative to avoid Real Audio, and the BBC will be dropping it soon anyway, as their players are revamped.

I happened to get a decent speaker system bundled with a PC some years ago, but even they only work as a system, and using the small speakers alone is still terrible. I tried them as an alternative to a laptop's own speakers which I had deemed awful, and changed that judgement to 'not really all that bad' after comparing to the external pair. The only problem with the laptop on a proper comparison was the lack of bass. Comparing them properly to bigger speakers showed the rest to be acceptable.

I just pipe it into the hifi amp now, if I want something a bit better.