Solved! Lenovo G500s not working after back cover replacement

[CSC1]

I purchased my Lenovo G500s in 2013. Over the years it had lost few screws on back and the back cover (chassis) was also broken. I tried replacing the back cover myself with a new one ordered from Amazon. It was working perfectly fine before replacement but after replacement its giving me following issues-

1. The screen is blank after pressing the power button, though the power LED and battery LED are glowing white. On connecting with an external monitor through HDMI I am not getting any video output on the external monitor also.
2. The laptop is giving a beep sound on removing the charging plug and also on re-inserting the charging plug every time.
3. After removing the back lid I could see that cooling fan and hard-disk are running and GPU and CPU are warm on touch.

What can be the possible issue? How do I solve it. I disconnected the LCD panel connector and reconnected it but still its not working.

 

[AlHuneke]

Did you observe any anti-static precautions when you took the cover off? Did you touch anything inside the unit? It's possible you "zapped" something.

 

[CSC1]

Did you observe any anti-static precautions when you took the cover off? Did you touch anything inside the unit? It's possible you "zapped" something.

No I did not. As far as I remember my feet were touching the bare floor all the time. Is it repairable? What do you think?

 

[AlHuneke]

I couldn't venture a guess as to whether it is repairable. I can imagine one of four things happened:

1. It just happened to pick this exact time to fail!
2. When you opened and closed the unit something (e.g. a connector) was disturbed.
3. In fact there is ESD (static) damage. Bare floors are not necessarily conductive (we had special floors in the labs where I worked).
4. There is some reason the case back itself is causing a problem. Did you try to start the machine with the cover off?

Good luck. Sorry I can't be more definitive. I would have done what you did trying an external monitor. If you still have an old mechanical hard drive, you could put your ear on it and hear if the machine accesses the disk on startup. However, this would not tell you how to make a repair. Sorry.