1. Click Start , click Run , type cmd in the Open box, and then OK.
Note On a Windows 7/Vista-based computer , click Start , type cmd in the Start Search box , right-click cmd.exe , and then click Run as administrator.
2. At the command prompt, type the following commands, and press
ENTER after each command:
regsvr32 /u softpub.dll
regsvr32 /u wintrust.dll
regsvr32 /u initpki.dll
regsvr32 /u dssenh.dll
regsvr32 /u rsaenh.dll
regsvr32 /u gpkcsp.dll
regsvr32 /u sccbase.dll
regsvr32 /u slbcsp.dll
regsvr32 /u mssip32.dll
regsvr32 /u cryptdlg.dll
exit
Note Click OK if you are prompted.
Note Microsoft Windows 2000 does not include the Sccbase.dll file. If you are running a version of Windows 2000, omit the Sccbase.dll file.
3. Restart your computer.
4. Click Start, click Run, type cmd in the Open box, and then click OK.
5. At the command prompt, type the following commands, and press ENTER after each command:
regsvr32 softpub.dll
regsvr32 wintrust.dll
regsvr32 initpki.dll
regsvr32 dssenh.dll
regsvr32 rsaenh.dll
regsvr32 gpkcsp.dll
regsvr32 sccbase.dll
regsvr32 slbcsp.dll
regsvr32 mssip32.dll
regsvr32 cryptdlg.dll
exit
Note Click OK if you are prompted.
After performing the steps given above try Installing DirectX.
Method 2 :
If you still cannot Install DirectX then there could be some corrupted files.
To determine whether the issue that you are experiencing is caused by one or more system files that are used by Windows Vista, run the System File Checker tool. The System File Checker tool scans system files and replaces incorrect versions of the system files by using the correct versions.
Follow the instructions in the link below to run SFC scan.