Firstly have you got a system restore point from before the problem arose you could try? If not, here are some basic straight forward easy to follow stuff that I would advise you to try first to help speed up your PC before moving on to more advanced stuff.
1) Ensure hard drive space is not approaching limit (right click C: and check pie chart)
2) Run Virus\spyware scan
3) Run disc clean up. (start\programs\accessories\system tools\disc clean up, use the more options tab also to delete all but the most recent restore points.
4) Uninstall any unused programs in add and remove programs (especially toolbars), donít uninstall anything you do not recognise without googling it first as you could end up uninstalling an important driver etc.
5) Run defrag when all above is done (start\programs\accessories\system tools\disk defragmenter). This can take a long time to complete if your drive is badly fragmented, so run this when you do not need to use your PC.
6) More memory is always a good way to speed your computer up.