Hello,
-Your laptop could be slow because it can be affected by a "Virus".
You can use Adwcleaner to find some problems or virus on your laptop.
And CCleaner for delete temporary files, registry error etc...
-Your laptop can be slow because it can be dusty.
You can remove the bottom panel and clean your motherboard from any dust.
-> A laptop with lot of dust will be hot and will be slow.
-If you move with your laptop running you can provoc some damage to your hard drive.
-> Bad HDD is a cause of slowdown laptop
Several factors can cause slowdown on your laptop
:)