Dvd rom was working but it stopped and the sound system is also nt responding after installing xp

If the hardware is newer than XP itself (2001), manual driver installation may be required to properly detect all devices. The first driver to install after OS installation is the driver for your motherboard's chipset. This driver can be found either on the computer manufacturer's website or the motherboard manufacturer's website. Following installation of the chipset driver, install the drivers for storage, video, audio, and network adapters. Last install drivers for peripheral devices such as a printer.

You can find out if the driver for the DVD ROM is installed and working properly by looking at Device Manager. Launch device manager by clicking on Start Menu-->Run then typing this into the text field:

Devmgmt.msc

Then press Enter. Any devices that do not have drivers installed or have non-working drivers will be displayed with a warning sign next to them.

It is good practice to install drivers in the right order as Scleros described. For some drivers like the chipset driver or video driver, if they are missing you might not see an obvious failure like your DVD drive not working, but your system is still not functioning as well as it could be. Also, older/default drivers for some devices can have security vulnerabilities that are fixed in newer versions.