How to know when was Windows started or shutdown?

Question

I need to develop a program in C# find out when was Windows started or shutdown.

Is there a log file that I can read to know Windows start and shutdown times? Or do

Answer 1

System.Environment.TickCount has a 24.8 days limitation.
This is because TickCount is a millisecond value contained in a signed 32 bits value.

Windows API exposes these two functions:
GetTickCount - returns a 32 bits value - available from Windows 2000
GetTickCount64 - returns a 64 bits value - available from Vista/Windows Server 2008

You can use GetTickCount64 this way:

using System.Runtime.InteropServices;  

[DllImport("Kernel32.dll")]  
static extern long GetTickCount64();  

DateTime osStartTime = DateTime.Now - new TimeSpan(10000 * GetTickCount64());