I've spent a week trying to log into my NVR 4108 directly via the mouse and on screen keypad. I kept getting invalid password and it made no sense to me. I could get into the NVR using the Amcrest software from my PC but that's because it "remembered" the password but given that machines fail, I was concerned that I apparently had forgotten my password.
Well, I had NOT forgotten my password. upon close inspection after entering my password and clicking "Enter" on the keypad (which hides the keypad), there was an extra character mask in the password I entered. I returned to the keypad, hit the backspace to remove that last character, clicked back on the screen (away from the keypad) thus making the keypad go away and then the system allowed me to log in using my proper password.
Apparently, clicking that "Enter" key on the keypad adds an invisible symbol, presumably the CR (carriage return) symbol thus invalidating my password and triggering a rejection. It is quite possible that I set that password initially with the Amcrest software via my Windows interface and the enter key on my keyboard was properly transmitted without that extraneous character. If you encounter such a problem, I hope this helps.