4 beeps on start-up would indicate memory read-write failure. You may need to remove and reseat the memory on your computer. Please ensure that the system is powered off and the AC adapter and battery are removed prior to reseating the memory modules.
During installation or removal of any hardware, always ensure that all data is backed up properly.
Disconnect any telephone, network, or USB cables from the computer.
Disconnect the computer and all attached devices from their electrical outlets.
Please click on the link below for the Owner's Manual under 'Manuals & Documentation" where you will be able to see the steps for reseating memory on your Dell computer.