Did you upgrade Active-X before you installed your Soundcard drivers? This can cause problems in Win 2000 l've noticed. l had this problem one time and only cured it by reinstalling from scratch and making sure the active-x upgrade was made last of all, after all other drivers.
Try going to device manager (right click my computer, manage, device manager...) and seeing if any device has a yellow or red flag (which indicates trouble...) - by right clicking on items and choosing properties you may discover (and be able to correct...) any anomaly... it could be you'll find your soundcard appears there twice in which case you should remove both versions and reboot...
If that isn't the case then remove the sole sound device and reboot anyway, it will be rediscovered and reinstalled by Windoze on reboot - only this will give Windoze the chance to reinstall the drivers for W2000 as opposed to W98, or ask you to provide the path to the correct driver files...
However, l very much fearin your case, the upgrade process overwrites/duplicates files and that the W98 driver is still embedded for this device and that it's not able to function under W2000...
I would never trust an upgraded installation anyway (regardless that M$ actively recommend this route which l believe they only do in order to plot how many people are abandoning W98...) and would suggest you totally reinstall, booting from the W2k CD-ROM and reformatting the drive in the process to get a clean version of 2000 on your system for peace of mind...
Before you attempt anything make sure you have your sound device drivers for W2000 to hand... or download them from whoever makes your soundcard/mobo before you begin...
Either which way my advice will get it working again...
Ivan
