I ran the windows update, update drivers and BIOS, restore the system to the last availble point, and it worked. For me the problem was sudden restart when I open laptop lid and awake the laptop when it is on battery. These were some observations: SUDDEN SHUTDOWN AFTER: Sleep works fine, and it never shutdown (restarts) as I awoke it while the laptop is continuously on AC, and never on battery. when it was not on AC, or AC was broken in between its sleep period: WHAT I DID I ran diagnostic tests (F12), and hardware was OK - also if someone is facing the same issue Also see the BIOS options in Dell - although it is not necessary in this case but block sleep option should not be disabled 
BIOS shows ASF2 Force off - windows event logger states kernel power critical error. On studying powercfg /SLEEPSTUDY reports, it came to know Windows shutdown abrubptly everytime I wake up the laptop from sleep, while it is on battery. If it is on power, the power will never break. I am not sure if it is a hardware related porblem, as I didn't open it - although I did change some BIOS settings (which I cannot recall - but those weren't related to power). In BIOS sleep is not blocked, and I rechecked everything related to sleep and power and it is where it should be, or maybe I'm missing something. I have also installed keysight drivers of instrument control, after which I have observed this behavior, they are uninistalled now, but the problem persists. So, what steps should I follow to troubleshoot further.    If there's the problem with Windows I cannot clean install it; it will take too much time to setup the system again. 
ASF2 Force off