How to I get files off a laptop that has lost power?

plug it in to the wall socket that looks like a face. dont put a fork in it

Remove the hard drive.  Get a data recovery program that does a deep scan.  Plug the hard drive into the windows machine scan it recover all the file and save them.

Use a small screwdriver to remove the screws holding the cover on your computer

Remove the hard drive

Plug the universal drive adapter into the hard drive's data connection port.

1) get it to power up, either buy a new charger, or a new battery, or whatever you need to get it up and running. 

2) Remove the drive from the laptop and plug it into another machine as a 2nd drive, either internally or externally to read and retrieve files. 

3) Take it to a tech to perform one of the above for you. 

get a new charger and/or battery

Yup, plug it in or pull the drive and put it in an external case. Or it's tech time.

Either charge it up or if it is actually won't power up, take it to a tech.

I could also suggest removing the hard drive and using a USB-SATA adapter to connect to a working computer, but you would need some computer experience for that.