Here are some reasons why your computer may be running slow:
- Problems with the registry of your operating system. Registry is a very important part of your operating system and many problems result from faulty registry. Additionally, it is not easy to repair the registry, contrary to what many registry cleaners promise. That is why very often you will ahve to perform a format. However, if you have System Restore enabled, you can simply restore your registry to an earlier version. Just make sure to restore it to a date when your computer was not showing any signs of trouble.
- Fragmented HDD can be a source of problems as well. If your files get spread in a random way, then the time it takes to read them increases and you may eventually notice lower performance. Many experienced users recommend defragmenting hard drives every month. The default Windows defragmenter works quite fine, but there are also commercial programs that defragment very well. Some of them even perform this task automatically in the background. While there are many commercial defragmenters, you do not necessarily need them to defragment your hard drive.
You can always make a fresh Windows install as it usually works. However, it is a lot easier to follow the advice given above, because it will save you a lot of time. Remember that you can ask for advice if you have any questions.