Original post by: Dan ,
Often systems slow down when the hard drive is quite full. I do recommend leaving about 1/4 to 1/3 of the disk free as Windows (and most other OS's) use the hard drive space as virtual RAM as well as swap file space. So the first think here is go though your files and apps and throw away (or off load to an external drive) as much as you can. The next step is very important! make a backup on what you have left on your drive to an external drive (backup drive) this external drive should be dedicated for backing up and ideally at least 3 times larger than what your internal disk is so you can make multiple backup images. OK, now the tough part defraging the hard drive. Depending on the version of Windows you have Windows offers some basic drive defragmenting functions. Personally, I like using a 3rd party tool like [http://www.condusiv.com/products/diskeeper/|Diskeeper] as they tend to go much deeper and can offer other functions that are useful. After doing this you should be running faster. If you find the drive is failing then its time to get a new drive or think about upgrading to a new system. Don't forget to check your RAM the more RAM you have the less your system will use the hard drive for virtual RAM.