5-3 flashing could be the system board. Lets narrow it down a little. Try taking out the battery, hard drive, DVD drive if there is one and Wi-Fi card. If two RAM modules take them out and try one at a time in each socket.
Plug in charger, without battery and see if you still get the flashing light codes. If not them reinstall the Wi-Fi, HD, etc. one at a time until the flashing code comes back. That is the defective component.