Windows keeps a list of all the important messages in a file, and it may be that there is some useful information there (such as reports of major disk errors).
If you have XP then do as follows:
Open the Windows Control Panel, and then chose "Performance and Maintenance"
You should see an icon for Administrative Tools. Click on it. The Administrative Tools window opens.
There is an icon for Event Viewer. Double click on it and the Event Viewer window opens.
On the left hand side click on System, The right hand frame should list all your system errors (newest at the top).
Are there lots of Red Crosses with "Error" against them ?
Double click on the "row" with the error on it and a window opens saying what the error is.
You can use the arrows in the top right to step up and down through the errors.
Here is a picture of the Event Viewer window so you know what it looks like.
http://bertk.mvps.org/assets/images/Event_View er.gif