They don't work - no sound - do I need to download a driver?

You don't need any drivers to make the speakers work what you need is the audio chip drivers for your motherboard ( the model of which you have not mentioned ).At the bottom right hand side of your desktop next to the clock do you see a icon of a speaker ?. If you don't , your sound driver has not been loaded. If you have the motherboard utility disc the drivers will be on it. If you don't ,you can go to the motherboard website on the net and type the model number and download all the drivers necessary to run the PC.
Just remember after loading the drivers remember to restart the PC to make the application run.

Hi kra02,
In order to get your sound to work again you will need to download and install your audio driver on the machine again.
You mentioned that you have a Compaq, you can go online to the Compaq website to get your Audio driver and probably the other drivers for your machine since you reformatted then you need to install all drivers needed for your Compaq.
Check in device manager under control panel to see which drivers needs to be installed, then you can download from the Compaq site to have your machine running fine again.
Drivers that you probably will need to download is the Chipset Driver, Video Driver, Audio Driver, LAN or Ethernet Driver, these are drivers that are most important.
I hope this help.
Have a nice day,
mvincentc