Hello Brannok,
On most, if not all, retail laptops, the first partition, which should be normally hidden, is your Lenovo Recovery Partition.
If you can access the memory stick/s, remove it/them and with a pencil eraser, go over the contacts (both sides), replace making sure they're securely seated and see if that makes a difference.
Just to ease your mind a little,
The laptop shut down while plugged in overnight.
, should not have caused your issue.
I have a laptop that I leave plugged in all the time and has not caused an issue for the past 2 years.
One question that should have been asked at first is, what were you doing that the laptop shutdown, downloading, updating, do you normally leave it on all the time?
Don