Here are some reasons why my computer runs slow, try the solution, you might get luck:

Virus – Closely related to Spyware, viruses can wreak havoc on your system’s performance and severely limit your PC’s ability to do what you ask it to.

Typically, viruses get onto your computer via infected email or instant messages, although they can also be installed via applications or files that you download from file-sharing networks and other non-trusted web sites.

Manual removal of viruses is very difficult and rarely successful, and we strongly advise the use of a quality anti-virus program like Kaspersky Internet Security 7.0

System Start-up packed with too many applications (Start-up overload) – Over time, as you add more and more programs to your computer, many of these applications automatically add themselves to your Windows Start-up folder.

Additionally, these applications can add themselves quietly to a hidden area of your Windows Start-up system (accessed via the MSCONFIG run command). In extreme cases your PC will appear completely frozen.

Limiting the number of applications loading themselves at start-up can speed boot times considerably and increase overall system performance.

Manage your hidden Windows Start-up controls automatically with PC Washer (Recommended)Corrupted/Bloated Windows Registry – The Windows Registry is the master control center for your operating system and applications it runs. Corruption or overload registry issues can cause all sorts of pc performance problems, including poor application startup times, slow Windows start-up, extremely slow shut down, inability to resume from computer sleep and more.

Cleaning, compacting, and optimizing your Windows registry can go a long way to dramatically speeding up your computer’s performance, start-up and shutdown speed.Recommended: Download Registry Mechanic to run a free Registry scan now