|You should have had your drivers backed up on disc. If your video card is a Radeon HD 4850, go to the ATI site & download the appropriate Catalyst driver. And make sure you have .NET Framework installed.|
As for the rest of the drivers (motherboard chipset, sound, network, etc), either go to the motherboard manufacturer's website or if you have an OEM system (Dell, Gateway, HP/Compaq, etc), go to the system manufacturer's website.
You *may* be able to find even newer drivers at the chipset manufacturer's website. For instance, Realtek sometimes has newer drivers for sound or network than the ones available from the other two sources I mentioned.