I had a computer even older. It had only 95 MB of RAM, about, and 4 GB storage or something.
My only guess is either your computer has a virus or viruses that are slowing it down or it's just simply old and it might need either reformatting (or is it just formatting?) or needs to be replaced. I'd wait until other people respond to this topic before I make a decision if I were you. It's always good to get a second opinion. Someone else here might have a better idea of how to help you.
For reformatting, this should be free, I think, if you have the CD with the operating system on it. I could be wrong. I haven't reformatted myself, so I don't know if there's other things you'd have to do first.
If it's a virus, you can get free antivirus online. Since there are rogue antivirus (they are viruses themselves) out there, here's some legit antivirus that are all free: AVG, Avast, Comodo, Panda Cloud, Avira free edition, and ClamWin. Of those, AVG is the most popular I think.