Slow bootup times have always plagued many Windows computers, and it can often be tricky to figure out what causes it. Often times, it's as simple as a hard drive going bad. When hard drives start to wear out, the operating system can have difficulty reading all of the sectors on it. If it happens to come across bad sectors during the bootup process, it will have to repeatedly attempt to read that sector until it finally works. This can extend the time it takes to boot the PC up by several minutes.