Let’s start with the simpler things first. If your computer is chugging, too much software booting at system start may just be to blame. Before you take more drastic measures, clean up your startup by opening the Startup tab of Windows 8’s Task Manager, or typing “msconfig”—minus the quotation marks—in Windows 7 and opening its Startup tab.
While you don’t want to disable Windows processes or processes related to your hardware, ruthlessly eliminate anything else that you can identify if at all possible. You wouldn’t want to prevent your antivirus from launching at startup, but there’s no reason for Steam or Adobe Reader to hog your system resources except for when you explicitly need them.