There might be a lot of programs loading up when Windows starts. You can see them by pressing Ctrl-Alt-Delete on the keyboard after you start Windows.
You only need explore.exe and systray.exe for Windows to work. However there could be others - like anti-virus and printer control programs - that you want to keep.
To stop a program from starting every time Windows is started you can disable it using msconfig. There's a explanation of how to do this
here.
Before you diable anything though try these steps:
Scan for viruses -
online scanner here
Check for Adware or Spyware running on computer -
Download scanner on this web page
Try defragmenting the hard drive also.
Hope this helps you.