I've reformatted a Dell Dimension 4400 machine. It showed that I have all drivers installed on it but there's still no sound. I've tried Creative Labs, Harman Kardon, Voyetra none of them is working, any ideas?  

Unless the machine was purchased with an add-on sound card, you would need the driver for the integrated audio [sound chip on motherboard].
I assume you have the link, but include it here in case not.
http://support.dell.com/

I guess I know why it has no sound even the system showed me all drivers are installed correctly (My Computer > Properties > Hardware > Device Manager - all drivers are installed, no missing)
I think I'll need to download the BIOS driver which might inc. the sound chip driver but it asks for a diskette in order to continue.. it has been years since I last used the diskette.
Thank you very much.