- how long have you had the laptop?
* was the laptop plugged into the wall or running on battery?
I got couple ideas and similar experiences..
Lenovo hardware known for Power management settings
1- have you installed any new software or firmwares recently? and in addition to hdd change, how do you manage your power settings? I also have a lenovo (x1) and I found my computer doing the same thing (although mine does turn on when I forced shut it for like 10 seconds). turns out Lenovo is collecting complaints from customers who have trouble cycling their computers back on from sleep or hibernation because of hardware/firmware conflicts.
if your comp does turn back on, then change your power settings as closely as you can to their default options and watch for the weight of graphic processing. After I removed my custom "what happens when you shut the lid,etc" settings, I don't run into this problem anymore.
Rule out dead battery
2- have you noticed anything lagging about your battery life? ideally users should be able to observe diminishing capacity with usage duration and intensity. but maybe yours battery was on the its way and then experienced some shortage? remove the bottom panel and the battery (using proper methods) - uneven or misbalanced psu can damange rest of the computer with surges and what have you.
Power surge from your wall outlet?
3- one thing I've been experiencing first hand is the annoying power of faulty building wiring to destroy my batteries. if you had it plugged in , then one possible issue might be the constant ESD that accumulated to this moment. you see the slight sparking whenever you use the wall plug? if so you should look into a cheap voltage regulator (especially if you have long sessions under something as taxing as gaming).
let me know what happens, good luck!