When computer startup problems begin to slow computer down it is time to perform some computer maintenance. Startup problems can be caused from driver conflicts, registry problems, missing files, network connection problems, hard drive fragmentation, viruses, spyware, malware, and several other software problems that naturally result from running Windows and browsing the Internet. Every time you connect to a website you can contract viruses, spyware, and malware. You antivirus, malware, and spyware software needs to be up-to-date.
You can spend considerable time defragging the hard drive, cleaning the registry, cleaning out temp and old files, scanning and removing spyware and this should be done on a regular basis to keep your computer running at its optimum. I run a computer lab of 35 computers in a high school where the students have admin rights and can configure and install any software that they desire. The students need to have admin rights to complete labs that are teaching them ho to troubleshoot and maintain computers. To keep me from spending too much time daily restoring all these computers I simple spend about 10 minutes each morning restoring all 35 computers at the same time. This provides a fresh, up-to-date, highly optimized, and fast computer for the students to use. There are 2 products that I have used to accomplish this restore. One is free Open Source software called Partimage and the other is Norton Ghost. I like the Norton Ghost product because it can be run using DOS.
Some of my students ask why they need to learn DOS. I explain to them that Windows is the problem and DOS can be a great solution to the problem. DOS is easy and fast to boot and will run a number of troubleshooting and Windows maintenance software programs. It is hard to use a Windows solution to correct computer startup problems when Windows will not start or runs slowly.
The Reboot Computer website has some additional information that you might find useful.