Check the Cables
The yellow light may blink if there is an improper or loose connection between the console and a monitor or TV. Check to make sure that the video cables (composite, component, or HDMI) are secured tightly into the ports of both the console and the monitor or television.
Restarting
The console may simply need to be rebooted entirely. Power off the console and remove the power chord from the outlet. Allow the unit to stand for at least 30 seconds to ensure that all power drains from the console. Put the chord back into the power outlet and turn the console back on.
Reinstalling the HDD
The PlayStation 3's hard drive may be loose and require a securer connection. This requires opening up the console and voiding your warranty. The hard drive (HDD) may have a loose connection that needs to be tightened. It may also need to be removed and reinstalled for the console to recognize it. The HDD will need to be replaced in cases where it is damaged.
Sending it Off
The final option for fixing the yellow light issue is to send it off to Sony. Fill out an online form on their customer support page and ship the console out. There will be a fee involved if the console is out of warranty. You will either receive a fixed console or a replacement if the damage is too severe.
Prevention
Preventing the yellow light is easier than fixing it. Keep the console cool and in a well-ventilated area to prevent overheating. Consider keeping a fan on the console to keep it cool. Use a surge protector when possible to prevent power surges from shorting out circuits or connections in your console. Always keep the system secure and immobile to prevent the internal components from shifting around.