dxdiag.exe is a process belonging to Feardoor Trojan.
This process is a security risk and should be removed from your system.
If found on your system make sure that you have downloaded the latest update for your antivirus application.
Non-system processes like dxdiag.exe originate from software you installed on your system. Since most applications store data in your system's registry, it is likely that your registry has suffered fragmentation and accumulated invalid entries which can affect your PC's performance. It is recommended that you
check your registry to identify slowdown issues.