I'd suggest you run diagnostic tool on the system. It will scan for any possible hardware issue that might be causing the system to act up
1. Power off system
2. Power on system, quickly start tapping F12 key continuously. You should be diagnostic screen. After quick tests, run full tests as well. Please report back any error code.
" but the light on top of the computer flashes on and off, and wifi and battery buttons flash which are placed next to the keyboard"
Dell Latitude 3440 Owner's Manual - Page 50
The HDD, battery and wireless led also serve as diagnostic leds. A particular pattern helps isolate the source of the issue.
You have specified that the battery and wireless leds are flashing / blinking. What is the status of HDD led?
If its option 2, then download the service manual - link provided by other user - and remove and reseat the memory modules and test the system - if required - test each module in each slot. This will help isolate the faulty memory module. If nothing works, then the motherboard needs to be replaced.
Also, please click my DELL-username and write me a private conversation with the service tag and your contact details(Name and Email) for case records.
Let us know if you have any other queries.