Some things you can check...
1. Check the space available on your hard drive; if it's almost full, that could cause everything to run more slowly as Windows tries to create "virtual memory" files.
2. Once Windows comes up, right click the "My Computer" icon, then click "Properties" to see how many system resources are available. If you're down below 90% free just after a reboot, it's a sign that your registry is becoming too large and you may need to save your data, reformat, and reload Windows. Operating with less then 80% of system resources available can really make your system sluggish.
If the problem is just with Explorer, then it may be something with your connection. If the problem is happening with other programs, then it's probably something with your system.
Good luck with it!