Laptop turns off suddenly for no apparent reason

So suddenly one day my laptop turned off for no reason, it didn't shut down but entirely turned off like when we remove power cable for a desktop. It seems to be working fine after that and it didn't turn on but when I removed the battery and plugged it in it did turn on but it used to shut down if i play games like cities skylines and gta 5 (before it never used to turn off while playing these game 's) so I suspected overheating and I cleaned the fan and reapplied the thermal grease make it only worse when i didn't clean the fan it used to be there for at least 25mins but now it turns off as soon as i start a game and now with battery reinstalled it won't turn off but battery won't charge sometimes it says plugged in not charging, but it do charge by itself when I remove the power cable and put it back in or I have to charge when the laptop is turned off. please help me I can't figure the problem out and i don't know when it turns off while in normal use but it turns off immeadetly when I start playing a game. Laptop is lenovo ideapad z510 i54200m 8gd ddr3 ram, gt740m 1tb hdd windows 8.1 and windows 10 dualboot