All I can suggest is do a system restore to the time before it started playing up. You could also defrag using Defraggler, delete unused registry keys and temporary files with CCleaner and delete programs that you don't need but delete them thoroughly using a program which deletes the left over registry keys and files. Then see if you see any improvement.
If not, see what processes are running such and see if you can see anything obvious conflicting (2 antivirus programs). Hope this works for you