I just created a test app & it works fine using the below code;
Process proc = new Process();
ProcessStartInfo sinfo = new ProcessStartInfo();
sinfo.FileName = "cmd.exe";
sinfo.Arguments = "/c c:\\windows\\system32\\iisreset.exe myservername /start";
proc.StartInfo = sinfo;
proc.Start();
Things that may stop it working;
a) IISRESET is not installed on the local machine
b) You need to include the full path - the command prompt that you open may not include iisreset it it's path
c) The command prompt is not a local admin on the remote machine - an elevated command prompt is required on the local machine
Short answer is, you need to debug & test. If you get rid of your arguments & just open the command prompt, can you actually run the command?
Kind Regards