hi cpu usage

Hello good people of the forum

It’s been awhile since I’ve been here

But have an issue hoping someone could offer some advice

We have an older desktop  4600 still in use

Mostly for just emailing & surfing

Seem to have occasional problems on start up

It load fine but there are time when thee mouse moves freely

But will not open anything even the start icon

If I am able to finally open task mgr it seems the cpu usage

Is 99% so I closed some unnecessary startup programs

Defragged and ran virus programs

It does not happen all the time but enough to be a pain

Any suggestions

thanks