Look under the startup tab in Msconfig and see what is starting. Many third party applications put their products in there, when it is totally unneeded to have them available and resident. (Java update, Itunes, Acrobat etc)
However, if this is a new installation, it could be the index service initialising, (This will quickly improve, but I have never encountered a 4 minute delay!), or it could be the defragmentation utility. But this is normall,by default, only one day a week.
My personal view is, (apart from what you may find in MSconfig) that you have your anti virus configured for a partial scan, as an option. Fastest way to check that would be to totally disable the Anitvirus and boot up again.