Hi my name is ***** ***** I will be the expert working with you today to help and resolve the problem you have posted.
I am sorry to hear that you are having such trouble. I will try my best to help you out and resolve the problem as quick as possible.
how old is the Lenovo Flex?
What Operating System (OS) is running on the computer?
does this model has a removable battery?
Laptops do have removable batteries. Let me check this model.
I see this has an inbuilt battery.
Unplug the ac adapter from the laptop and then you push and hold down the power button for 45 seconds and then release.
wait for 2 mins and then connect the ac adapter and power it on.
Let me know what you get on the screen, it should boot.
does the mouse work?
press and hold down the shift key and then click on shutdown and then restart dont release the shift key till it shutsdown.
please unplug all external devices including the dell monitor
then restart computer
then check the keyboard and rest of the functions and let me know the status
pair it again. Remove the usb receiver and try to connect to a different USB port and withing 30 seconds insert the battery.