My monitor going to sleep mode if I connect to my nvidia VGA card card.
LG monitor saying "SLEEP MODE ACTIVATED" Red light is blinking
I connect to my on board VGA it's working properly....
The "sleep mode activated" message is normal on the monitor if it is receiving no signal from the PC (VGA card). You need to connect it to on board VGA and tell your system which card to use (or which order) in the BIOS. I cannot tell you how to get into BIOS since I do not know your PC brand/model.