HEAT and DUST
Will make them run slow and not perform properly.
The best thing is to keep your home between 68 and 72 degrees
laptops you still need to prop it up so the air can circulate?
If you have ceiling fans use them
Do not set up your computer too close to a Heat-AC register.
Clean out the dust from inside of the computer case
Check it every two months its a good thing, get a can of compressed air
Make sure the computer is disconnected from any power source
Use the air on the keyboards too. Invest in a laser lens cleaner disk for CD-RW or DVD-RW its well worth it.
Check for anything that looks Burnt on the motherboard, Look but do not touch the motherboard
Download Speedfan to check Heat | Click on these pictures of Heat to see a bigger picture