In case of windows, install only those softwares which you need. Don't mess up ur pc with all useless stuff. Check for registry errors and fix them using a good software like regcure or registry booster. Don't forget to check whether your antivirus is updated or not. Outdated antivirus often tends to slow down the system. Use ccleaner to remove the crap. Don't exhaust your ram by using too many programs in background. Turnoff windows sidebar or desktop enhancement softwares if you don't need them. Scan all system by updated virus to make sure it is not infected. Also disk defragmentar etc. small utilities can be helpful for your pc.

In case of Windows, install only those software which you need. Don't mess up your PC with all useless stuff. Check for registry errors and fix them using a good software like regcure or registry booster. Don't forget to check whether your antivirus is updated or not. Outdated antivirus often tends to slow down the system. Use CCleaner to remove the crap. Don't exhaust your RAM by using too many programs in background. Turnoff Windows sidebar or desktop enhancement software if you don't need them. Scan all system by updated virus to make sure it is not infected. Also disk defrag etc. small utilities can be helpful for your PC.