XPS 8500, no signal detected on monitor

If you are not sure if the video card is the problem, pull the GPU and connect the monitor to the Integrated video port. Then boot and see if you get a video signal. The CMOS battery is not likely a problem unless you have had problems with time and date needing to be reset. But based on the age of your system I would replace the CMOS battery just  to confirm that the battery in the system is new and not a problem.

it is too quick to point to video card as suspect when XPS 8500 does not POST.  statistically more often it is motherboard or psu.

what is color of power button led? Solid white is good. Amber not good.

have you done a bist test of psu?  if not do it to test the psu.  if psu is good, to r/o cmos issue, start w replacing cmos battery w a brand new battery then clear cmos settings via motherboard RTCRST  jumper.

if still no video, remove all memory sticks.  does pc beep when powered on?  beep and beep are good. no beep at all not good.

Have you checked the cable connections at the monitor and at the PC?

Can you test this monitor on a different PC or a different monitor on this PC?

Had same issue with my XPX 8920. Open it, removed the battery, as sugested by some, pushed power bottom and hold for 20 scnds. Of course make sure you disconnect all external  cables from the tower, and grounded yourself by tapping on the power supply  case to discharge any electricity from you. Place battery back  in  showing it's identifications ( + ) facing up. Than unplug cable that supply  power to the monitor. Conect power cable to the tower and monitor, than all other communications cables, keyboard, mouse, etc. Power PC On, let it cycle in and out, my took about 5 minutes, and all came  back to normal. You can try just disconnecting the monitor power, and reconect it, but make sure the Tower is off during this process.. If doesn't  work do the battery. Good luck. 

Hey man, good luck. I've owned mine since 2012/2013 and had this problem every time the power goes out or I turn it off. Something if with their hardware that I guess they are keeping secret lol 😂 

<Profanity is never needed nor allowed on our Forum. DELL-Admin>

@ProfessorW00d​ it would be, however there is no fix to this problem. Point blank period.between me, OP, and another post I found on dells site, there is literally no fix for this. Just myself have replaced the PSU, GPU, ram, battery, and hdd. I've taken this PC apart and reinstalled everything. Something isn't right with the XPS 8500.

<Profanity is never needed nor allowed on our Forum. DELL-Admin>

I'll go ahead and go on record. After two weeks since my house lost power during a storm and cut off (Dell XPS 8500) couldn't get it to boot from anything except the on board card. After many many boots and turn offs (200+) I'm finally sitting at my login screen as of 2 mins ago. 

The best answer no one will give you is the classic "turn it off and back on again" 

Dell use to be a respectable brand.