So my computer was downloading the newest windows update and I left it, alone for a few hours but it ran out of charge before it finished updating and now when I try to turn it on, even when I plug the charger in(which works) it dies. Please help
Never a good idea to try and do an OS update or upgrade on a laptop battery! That's a sure fire way to kill your windows.
That being said, it's customary to tell us a few things about your computer, such as the Make/Model. That being said the latest W10 AU update that's being pushed out to W10 customers named (KB3176936), dated Oct. 1 2016, is wreaking havoc with our W10 users. I just wrote a detailed post about it last night, and it contains many solutions that will help you recover from your problem.
Hopefully, prior to letting this W10 AU update come into your computer, you've created at least 1 backup of all your personal data (Library folders) to external media somewhere. If you didn't you are at risk of irretrievable data loss while trying to repair the damage done to your laptop by the update. Here's the link to my Post: Windows 10 - After scroll cursor points the beginning.... Take a look at my POST #4.
In the event that you do have your personal data backed up to external media, I'd suggest trying to "rollback" windows to a point in time prior to the update coming in, 2-3 days or a week say, and use the built-in windows System Restore to rollback your windows to get it working again.