Right Click My Computer - choose Manage - this will open the Management Console
In the Left Pane open System Tools and then Open Event Viewer
Then click on Applications - look in the Right pane - scroll to the relevant date and time - this might give you some idea of what's been 'going on'
If you find anything which is useful - stretch the window right over to the right and make a note of the Event ID number and also the Source
Double click on the entry and a box will open that will give you more info
If you find anything 'useful' then go here:
www.eventid.net and run Search for the Event iD number