XPS 8700, GeForce GTX 645, connection

@Lorna411 from what you wrote it appears that your XPS 8700 has a DVI-I output. A DVI-I has both digital and analog signal outputs versus DVI-D which only has digital signal outputs. The DVI adapter for the HDMI cable should have worked. Did you use the monitor's On-Screen Display (OSD) menu to select HDMI as the Input Source (Auto Select should have also worked)? The only other reason I can think of why the DVI adapter did not work is that the XPS 8700 has DVI-A (only analog signal outputs), but that seems to me to be unusual. If your XPS 8700 has HDMI output, then the HDMI cable that came with your monitor should have worked, no adapters needed, again check your OSD settings for Input Source.

VGA cannot use converters. VGA is analog while hdmi and dvi are digital. You might be using the wrong connection since the xps 8700 has both a video card and integrated video. You need to use the video card to connect a monitor. The video card is at the bottom on the back of the tower in one of the horizontal slots. The integrated connections on the upper left middle cannot be used. See the manual-- HERE

Use an hdmi cable to connect the monitor.

And keep in mind that these adapters may only work in one direction, so you just can't flip them around and expect them to work.

You need to get an adapter that is specifically designed for PC(HDMI)>Monitor(DP). 

I would suggest DVI to HDMI cable or HDMI to HDMI

You have all 4 types.

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

https://downloads.dell.com/manuals/all-products/esuprt_electronics_accessories/esuprt_electronics_accessories_monitors/dell-s2421hs-monitor_setup-guide_en-us.pdf

https://www.amazon.com/4K-HDMI-Cable-10-Compatible/dp/B01N22LFPL/

https://www.amazon.com/Rankie-Cable-Rated-Speed-Bi-Directional/dp/B00YOSA85Q/

DVI -I  is digital

DVI-A is analog and has C1 C2 C3 C4 pins

DVI-I can be bi directional EXCEPT there is no audio.

Digital only DVI does not have the extra 4 pins for ANALOG VGA

NOTE THE VGA PINS DVI -A

Works both ways

@speedstep wrote, "DVI-I is digital". From the Digital Visual Interface Wiki, "DVI-I (integrated, combines digital and analog in the same connector; digital may be single or dual link)".

Lorna411,

Your XPS 8700 shipped with the added Nvidia GeForce GTX 645 video card.

Nvidia GeForce GTX 645 video out ports = DP/HDMI/DVI-I
S2421HS video in ports = DP/HDMI

Nvidia GeForce GTX 645 HDMI out port --> S2421HS HDMI to HDMI cable --> S2421HS HDMI in port

Not sure what you are trying to say. What do I need in the way of an adapter?

@Lorna411 You should tell us what ports the graphics card on your XPS 8700 has. DVI? HDMI? DisplayPort? You mentioned you tried a DVI adapter for the HDMI cable, that should have worked. Did you check the On-Screen Display menu setting for the Input Source?

As Dell-Chris M said you should be able to use either an HDMI cable (both ends) between the PC(video card) and the monitor or a DP cable (both ends) between the PC(video card) and the monitor. So you shouldn't need any adapters.

And as @Vic384 said, just make sure the monitor is set on its On-Screen Display to use the right type of port, based whichever type of cable you use...

Chris, I did what you suggested. I plugged the HDMI into the port on the monitor, then into the HDMI Monitor Connection Port on Graphics Card (#12) port on the XPS 8700 Desktop Computer. HDMI is selected on the monitor (having pressed the button on the underside of the monitor to make sure it was selected). I then turned on the computer but I am still getting “no HDMI signal” on the monitor's screen and then the message that it is going to standby mode. What am I doing wrong?

Yes, the monitor was turned on first before the computer. Don't have a DP cable but I do have a DP adapter. One of the Dell Support people told me I needed a DP adapter. To plug it into the DP port on the monitor and then the HDMI cable end into it and then to plug it into the HDMI port on the computer. That doesn't work either. In fact, I got an error message saying there is "no DP signal". No idea if the video card died. The monitor that came with the XPS (2013) died a view weeks ago. Everything went green on it so I thought it had died. The computer was working fine. I could access my files and also send emails and watch videos so I don't think that is the problem. It was just that the screen was green.

@Lorna411 Did you also try using the button (Shortcut key: Input source) on the underside of the monitor to try selecting Auto select as the Input Source?

Was the monitor turned on first, before the PC?

Can you test with a DP cable?

Did your video card die?

I did that but it will only let me choose HDMI or DP. I slide the bar up to Auto and press the check mark, but it won't accept it.