All right, It would help to know what you already did that worked temporarily, but the codes you describe indicate a problem with the BIOS/Power/Memory you say it was unused for a time, I would not expect your CMOS Battery to be dead after only seven years, but it is a possibility so if the fix works but it repeats, you may need to replace that battery. First. though, go to Dell's webpage (link below) and the simplest thing is to just watch the video on how to fix POST errors. Or you can read the information there that tells you in greater depth but the video does an excellent job of putting it in a nice capsule format. Going by the error codes I'd also try re-seating the memory if the problem persists (just make sure the memory is properly seated and run a memory test if you get the BIOS working to see if it's a problem) Did you replace the Laptop Battery as well. since it had been stored? Anyway try that, if no joy, let us know and explain what you did that worked too so we can try again, Okay? Here's the link:
https://www.dell.com/support/contents/en-us/videos/videoplayer/how-to-do-no-post-troubleshooting/6308317772112
Good Luck!