Your Laptop MAY have a overheating problem? The internal fan(s) tend to pull dust and dirt inside and CLOG and prevent proper venting and circulation!
Try your laptop on a flat table surface and see if that helps?
OR ~ OPEN your CD/DVD Drive... HOLD IT OPEN and power-down... REMOVE the battery...
Put a plastic bag over your DVD Drive to help keep dust and po*p from contaminating your Laser optics!
*Take goggles or some means of eye protection with you....
Take your Asus to a tire repair shop and blow it out REALLY WELL! Blow air DIRECTLY into ALL vent holes and INSIDE... JUST PAST the DVD tray opening.
You MAY need to remove the bottom cover to access the REAL dirt and junk... Here is a Link that WILL help you ~ not for the weak of heart!
ASUS G73J G73JH laptop screen replacement procedure