You need to user Event Viewer. Easiest way to go there is to click the Start Button and type "eventvwr".
Now click on System for System events.
Only problem is there are so many.
You need to click the filter button (or go via the menus).
Here, you can type in the event types that you want to filter by.
For example, event 1074 says when a shutdown was initiated and why.
This worked for me today but there are far better ways to get this information now that I'm back home and looking into greater detail. Check out this petri.co.il (one of the best PC support sites on the internet for many years) here:
- Task Manager
- System Information Utility
- Uptime Utility
- Net Statistics Utility
- Event Viewer
Check Uptime In Server 2008