About the only thing left is a bad system board -- which is going to cost more to replace than the system is worth. Time to recycle and replace the system.  
I wonder if someone can advise me, please? I have an Inspiron N5030 which has been doing a great job for a long time and is [was!] in daily use. It powers up for about 4 seconds, during which time the CPU fan fires briefly and the DVD player spins up, and then the white power LED goes out and it shuts down. Pressing start again repeats the process.These responses are quite normal but the device isn't running long enough to get to a diagnostic stage.   Clearing residual power with the PSU and battery removed and holding down the power button for 15 seconds has had no effect. I have checked the 2 RAM modules for seating, the SSD has been substituted and the  CR2032 data retention battery checked [ a replacement was tried ]    All wiring and connectors appear OK but I am stuck. I wonder if there are any other options left? Wise guidance will always be greatly appreciated!
N5030 not firing up