when trying to install DirectX 9.0c:"A cabinet file necessary for installation cannot be trusted."

Register the following DLLs to troubleshoot this issue:

1. Quit all programs that are running.
2. Click Start, and then click Run.

3. Type "regsvr32 urlmon.dll" (without the quotation marks), and then click OK.
4. When you receive the "DllRegisterServer in urlmon.dll succeeded" message, click OK.

Repeat inputting the following commands and click OK after each command.

regsvr32 shdocvw.dll
regsvr32 mshtml.dll
regsvr32 browseui.dll
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 cryptdlg.dll

5. After registering the above files, restart the computer and check whether the issue is resolved.