Slow Running Computer

My computer is finally running slow after almost 9 years. It has been reformatted several times during these years. It is a home made computer a friend made for me, but it is becoming unbearable to use.

I don’t believe I have a virus, as there is no signs of one both obvious or any that my virus protection picks up. I am starting to think that perhaps the RAM and other components inside have finally "wore out"

Any help would be appreciated.

Tom