computer slow down

Does anyone know the answer to these?
why is my computer (especially Yahoo) so slow when comes to clicking on a link to go somewhere? it feels like cabin fever if you understand.

Why doesn’t my defrag program defrag like it is suppose to do?
it won’t continue to defrag, it just stays there and will not do its job, slowly as a matter of fact; then it tells me it is completed when it isn’t. when i view the report, it still shows folders that aren’t defragged, put in place.