To access Event Viewer go Start - type
eventvwr then press enter.
You will have to wait for it to read the logs and then you will be presented with a list for Critical, Error and Info etc.
Hopefully you won't have any Critical but click on Error then on View All Instances of This Event in the right pane then look for errors with the date and time stamp when you had the problems.
Clicking on those will produce a brief explanation of what has stopped etc. with an Event ID.
If you find any applicable then click on Copy in the lower right pane and select Copy Details as Text and then you can paste it in the Reply box and Shane should probably be able to help you with those.
There's a blue Online help link you can click on which may or not give more info/solution.
Reliability history may also have something on this and is accessed by going Start - type
reliability (or part of) then press enter as View reliability history will be highlighted.
Clicking on any red crosses or info for each date that has either of these will produce a report with a blue link for more info.
This article will give you more info on using the Event Viewer in Win 7 although some may apply to XP/Vista (don't know Win 8)
http://www.techrepublic.com/blog/windows-and-office/use-windows-7-event-viewer-to-track-down-issues-that-cause-slower-boot-times/