Elite book 2640 blue light light on,yellow light flashing,screen blank

Yellow light sounds like charge indication.If you press the power botton the fan should spin and you should be able to open the DVD by pressing the button on the tray.These are 1st steps to check motherboard function.If there is RAM installed remove battery after turning off power supply.Open memory door and reseat RAM.Replace cover then battery - power on.Any picture?Try an LCD monitor - no picture? Try different RAM or 1 stick at a time,remember to remove battery or RAM will be damaged.Still no picture - remove battery and try with AC adapter only.Still no picture - remove AC hold down power button for 30-sec plug in AC only and press power button.Still no picture - check CMOS battery if it uses a CR2032 button cell it may be flat.This can cause a no boot situation.If the CMOS has a plug or is soldered to the board that should be OK.The button cell may be hidden in the chassis anyway and to change it will require disassembly.So replace it when doing the cleaning.Still no picture - GPU is faulty.The unit should be disassembled and a reflow of GPU done,as well as cleaning all dust and fluff from the fan and other cooling system components.Airflow restriction of the cooling system is the cause of overheating and GPU issues.Google disassembly for your laptop and reflow method for GPU.If you have no experience with disassembly a step by step guide is crucial.Breaking parts is easy so extreme care is very important.