Answer: Usually Windows will leave a log behind during a the crash / reboot phase called a dump file (.dmp file).
- This .dmp file is located in C:\Windows\System32\Minidump.
- Grab the dump file with the latest date on it and drag it to your desktop.
- Open a web browser and go to http://www.osronline.com/page.cfm?name=Analyze
- Near the bottom of this page click choose file and then click upload dump.
- The file will be be analyzed and should give you a clue as to why your computer crashed
Below is a video I made outlining the steps above: