DirectX is a set of multimedia Application Programming Interfaces (API’s) written by Microsoft. It is a collection of Dynamic Link Libraries (DLLs) that contain functions useful to a wide range of multimedia programmers, but are all almost entirely platform independent. This allows programmer’s access to fast graphics, sound, and input functions while not needing their apps to test for the capabilities of the computer on which their program is running. DirectX will evaluate these capabilities and if they are not present, DirectX may attempt to emulate the functions in software instead of hardware.

Major Components
the following are the major components that make up DirectX:

• DirectDraw – 2D Graphics

• Direct3D – 3D Graphics

• DirectSound – 2D Sound

• DirectSound3D – 3D Sound

• DirectMusic – Music

• DirectPlay – Network/Multiplayer

• DirectInput – Input Devices

By default, the Windows XP system is shipped with DirectX 8.1, which can be upgraded to DirectX 9. If one or more of the following errors messages is displayed, on your Windows XP PC, you may have to first uninstall DirectX 9 and then reinstall it. The latest version of DirectX is DirectX 10 that can be installed only on Windows Vista. The last version supported on Windows XP is DirectX 9.

The first step to fixing Direct X errors is to see which version you have installed on your system. Click the Start menu, and then choose Run. In the box type dxdiag and press enter. A new Window will appear and your version of DirectX will be listed at the bottom.

Common Direct X Errors

- Cannot initializes dinput9.dll.
- Fatal exception error in dplayx.dll.
- A required DLL file, D3D9.DLL, was not found.
- dplay.dll has performed an illegal operation.
- Access violation error in Direct X files D3D8.DLL.
- This application has failed to start because d3d9.dll was not found. Re-installing the application may fix this problem.
- Unable to find file d3d8.dll, ddraw.dll or d3d9.dll.
- No display at all on the screen.

To fix most of these problems, all you need to do is make sure that you have downloaded the latest version on your system. First you should uninstall the DirectX and then install the new version of DirectX, for Windows XP you can download the latest version from here

Uninstall DirectX:

1. Start -> Run
2. Type Regedit and the click enter
3. Navigate to the following registry key. HKEY_LOCAL_MACHINE\Software\Microsoft\DirectX
4. Delete the DirectX folder
5. Exit the Registry Editor, and restart your XP computer.

During the system startup, after the restart, your system will reinstall DirectX 8.1 that is originally shipped with the Windows XP operating system. To confirm this, run the dxdiag command from Start > Run. The command will open the DirectX Diagnostic Tool utility. This utility provides you with a lot of information about DirectX installed on your computer along with the version currently installed on your system.