One of the most common questions I get is what can you do about a PC that takes ages to boot. The older a PC the more likely it is to slow down with the stuff that Windows leaves behind in everyday use and from installing and removing applications.
A couple of goods steps here are  clear out the rubbish on your PC (temp files, unwanted registry entries etc) and  stop unnecessary programs from loading.
I use CCleaner regularly to clear out the rubbish plus Mike Lin’s excellent StartUp Control Panel to stop unnecessary programs loading at startup.
I’ve never had any problems with these applications but it’s always good to set a System Restore point in Windows & backup your registry (CCleaner offers this as an option) before making any changes to your PC’s configuration.