Any slowdown on a computer would be caused by software, not cpu. Virus, spyware/adware, corrupted drivers cause slowdowns. This can be fixed by reinstalling windows or trying System Restore. Make sure that other hardware (like old hard drive, not enough ram) does not cause bottlenecks. Ram should be matching, including Cass Latency (CL), so the ram does not run at lower frequency than it could, etc.