From lordbob above
To do this, hit start, and type msconfig and hit enter. This will bring up a diablog box with boot options on it. Choose Diagnostic Start Up (or boot) and restart your computer. This will disable all non-essential drivers
, programs, etc and allow you to enable them one at a time until you find the culprit.
Go to search, type the word msconfig and then hit enter. I think the rest of Lordbobs explanation is clear. If you have a question about a specific part of it just ask.