S3220GDF, scanning for signal during use

Hi. On Friday (26th) my S3220GDF suddenly stopped working. I got in contact with Dell and they sent me a new one. Though, since I received I have been experiencing two things.

First, on my MacBook, the S3220GDF keeps scanning for signal during the use even though I am already connected. I use HDMI on a MacBook 2017 with an adapter. No, it's not the adapter and not the cable. I tried different cables/adapters and I used the same laptop, same adapter on another monitor for 8 hour and didn't have any trouble. I also tried the second HDMI port on the S3220GDF. 

Second, on my Windows (GPU GTX 1070), connected with DisplayPort, as soon as I changed the input to DP on the S3220GDF, I saw that ugly 640x480 resolution. I tried everything, reinstall drivers, update Windows, but it doesn't let me select any other resolution rather than 480p. Whenever I connect my Windows with HDMI, it works 2k. Also, when I open the Nvidia Control Panel and I go to "Adjust desktop size and position" The resolution and refresh rate list are empty.

Can anyone help me?

Thanks