NEED HELP with fixing up a computer

Hi.

So I have this computer that I have connected to my living room TV, and I use it to watch videos and such.

It hasn't been in such a good condition lately, and it is actually about 5 years old.

I want to change some parts in it so that I can run it more smoothly.


What I want to know is, what parts would I generally need to replace?

I'm thinking about replacing the CPU and Motherboard so far, but I was wondering if there were anything else, like an internal hard drive that I need to replace.

Does it matter if the internal hard drive is old? What parts need to be replaced if they're old?

That's pretty much what I need to know.



Thank you!