My name is Anue and I work for the Social Media and Community Team at Dell.
From your post, we understand, that the computer wouldn’t Boot.
As you confirm, that the Hard Drive installed on the computer works fine. You also have stated, that the Memory as well has been.
The issue that you are facing could be an issue, caused by the new Memory installed or the way its installed, as the computer doesn’t into the BIOS as well.
Kindly the try the following steps and check if it makes any difference.
Turn off the laptop and remove bot the battery and the charger.
Press and hold the Power button down for around 30 seconds, to remove all power of the laptop.
Remove the newly installed memory and try using the old memory cards.
If the computer works with the old Memory cards, it confirms that the new memory cards are causing the issue and hence you could try re-seating the new Memory cards.
Try the new Memory cards one at a time.
Kindly reply for any other queries, we would be glad to assist you.
Thanks & Regards
Dell Social Media Responder