Please do try to reseat them RAMs.
- Remove them all for couple of seconds then put them back in making sure that they are seated properly in to each slot.
- If you'll still hear the beeping sound, do clean the inside of you laptop to make sure there's no dust stopping the fans from spinning freely.
- Also do test your laptop without it's battery just use the charger and see if it will still beep without the battery connected.
-If all these will not work and if your laptop is still under the factory warranty do contact Dell support for a repair because it can also be an indication of a hardware failing.