How can I list all processes running in Windows?

This is how I prefer to access the processes:

static void Main(string[] args)
{
    Process.GetProcesses().ToList().ForEach(p =>
    {
        Console.WriteLine(
            p.ProcessName + " p.Threads.Count=" + p.Threads.Count + " Id=" + p.Id);
    });

    Console.ReadKey();
}

Finding all of the processes

You can do this through the Process class

using System.Diagnostics;
...
var allProcesses = Process.GetProcesses();

Running Diagnostics

Can you give us some more information here? It's not clear what you want to do.

The Process class provides a bit of information though that might help you out. It is possible to query this class for

• All threads
• Main Window Handle
• All loaded modules
• Various diagnostic information about Memory (Paged, Virtual, Working Set, etc ...)
• Basic Process Information (id, name, disk location)

EDIT

OP mentioned they want to get memory and CPU information. These properties are readily available on the Process class (returned by GetProcesses()). Below is the MSDN page that lists all of the supported properties. There are various memory and CPU ones available that will suite your needs.

http://msdn.microsoft.com/en-us/library/system.diagnostics.process.aspx

Code:

Add this line to your using list:

using System.Diagnostics;

Now you can get a list of the processes with the Process.GetProcesses() method, as seen in this example:

Process[] processlist = Process.GetProcesses();

foreach (Process theprocess in processlist)
{
    Console.WriteLine("Process: {0} ID: {1}", theprocess.ProcessName, theprocess.Id);
}

Finding all processes is rather easy actually:

using System.Diagnostics;

Process[] processes = Process.GetProcesses();

foreach (Process process in processes)
{
    // Get whatever attribute for process.
}

JaredPar already pointed out the Process class, so I'll just add, that you should be aware, that the class takes a snapshot of the process' information when the instance is created. It is not a live view. To update it you have to call Refresh() on the instance.

Also keep in mind, that the process may close while you are inspecting it, so be prepared to catch exceptions and handle them accordingly.

And finally if you call Process.GetProcesses() you will also get the pseudo processes "idle" and "system". IIRC they have specific process IDs so you can easily filter them out.