My computer is quite old now, and has been getting slower and slower. Last week, it had declined to the point where it was almost unusable at times.
I asked a friend if he knew anything about speeding it up, and he suggested "C Cleaner" a free online download.
Off I went to the Internet and downloaded it (it took abot 30 seconds).
Before starting it, I checked my hard drive and found that there was 22Gb of free space left. The "Clean up" took 3 days, during which time I couldn't use the computer whilst it was doing the cleaing. It could, however, be stopped if I wanted to use it, and then started again after I had finished. After each cleaning session, the hard drive space increased. When it finally finished, on the third day, the free space had gone up to 65Gb, but it still didn't seem any faster.
I then ran a standard defragmenting that took about 30 hours (It normally takes only one or two).
The free space on completion had gone up to 87Gb, and the computer is now working like "greased lightning!" 
It is reborn, and I don't need to purchase a new one!
Just thought I would share this info with you.
Bob