This may help: .NET How to detect if DirectX 10 is supported?.
Edit:
Below is some better code I think. The best I can come up with is a check based on Windows version in the case of DX10 or DX11. This is not 100% accurate (because Vista can be upgraded to DX11 but I do not check for this), but better than nothing.
private int GetDirectxMajorVersion()
{
int directxMajorVersion = 0;
var OSVersion = Environment.OSVersion;
// if Windows Vista or later
if (OSVersion.Version.Major >= 6)
{
// if Windows 7 or later
if (OSVersion.Version.Major > 6 || OSVersion.Version.Minor >= 1)
{
directxMajorVersion = 11;
}
// if Windows Vista
else
{
directxMajorVersion = 10;
}
}
// if Windows XP or earlier.
else
{
using (RegistryKey key = Registry.LocalMachine.OpenSubKey(@"SOFTWARE\Microsoft\DirectX"))
{
string versionStr = key.GetValue("Version") as string;
if (!string.IsNullOrEmpty(versionStr))
{
var versionComponents = versionStr.Split('.');
if (versionComponents.Length > 1)
{
int directXLevel;
if (int.TryParse(versionComponents[1], out directXLevel))
{
directxMajorVersion = directXLevel;
}
}
}
}
}
return directxMajorVersion;
}