I do not know what you intention is for listing all running process in Windows.
Perhaps some remote status in Web ?
But anyway. If you want to list all running process and list all the loaded modules for a process, you need elevated permission.
A normal user cannot list all running processes in Windows.
A good inspiration is to look at the program Process Explorer
] from Microsoft. It can help you to verify what you are able to see.
And for a Web method, web sites.. What is your plan? REST API, SOAP, ASP.NET Site?