It is getting extremely slow. cursor works, but can't leave page.

Overall the laptop is getting extremely slow. At times, the cursor functions but it is impossible to click, because it does not leave the page your on, or you canot even operate the trackpad clicking unless you reboot with the button. This is a software issue. I’m just wondering what parts need replacing, and if you know any good websites where to find parts for this laptop. Thanks a lot! :)