First, install the Windows 8.1 compatible monitor driver. 

<ADMIN NOTE: Broken link has been removed from this post by Dell>

Restart the laptop when done. See if doing this fixes the issue while using the laptop HDMI out --> HDMI to DVI cable --> U2412M DVI in

If still no go, the U2412M shipped with a VGA to VGA cable. Test this and tell me what resolution is shown =
Vostro 3750 VGA out --> VGA to VGA cable --> U2412M VGA in

Regardless of ports used, the U2412M is maxed at 1920x1200. The Vostro 3750 was not validated by Dell for Windows 10. This HDMI issue could be part of that non-validation. The HDMI issue could also be the laptop video card driver. You should ask the guys on the Laptop Video board.

Using the exe installer didn't work. Installed the drivers manually but HDMI output stayed at 1024x768. Connecting with VGA set the resolution to 1920x1200.

Can we make it work with HDMI->DVI? I suppose there is a difference in the display quality between hdmi->dvi and vga->vga at the same 1920x1200 resolution?

The same issue existed with Windows 7 too. I've posted in the Laptop Video forum and will follow it up there.

Thank you Chris.

Hi,

1. Running "Dell Monitor Driver Installer" gave the following message:

The following connected monitors have been detected:

       LG Display Plug and Play Monitor - LGD0303

       Def Plug and Play Monitor - Default_Monitor

Drivers for the following monitors have been found:

       Dell U2412M(Analog) - DELA079

       Dell U2412M(Digital) - DELA07A

       Dell U2412M(DisplayPort) - DELA07B

Drivers for the following connected monitor can be installed:

       None

2. I installed the 3 drivers - analog, digital and display port manually and restarted as well. But the resolution was still stuck at 1024x768.

3. Connecting with the VGA cable, the resolution was at 1920x1200.

Is there a way to make it work with the HDMI->DVI as well? I suppose the HDMI output will be better than VGA at 1920x1200?