Gtx 660 Problem

I just bought an asus gtx660 for my kids Dell XPS 8700. I took out the gtx745(oem) which has the same drivers as the 660 and I'm getting no signal with the 660 installed......shouldn't this work easier than this?

 

Tell us more about this system - be sure to include the power supply.

Did you ensure you connected the auxiliary power cables?

Did you unplug the computer from the wall before removing the old card and installing the new?

 

It's an XPS 8700
i7 4790
Had gtx745 oem (still works fine,tested it about 1hr ago)
16gb of ram
Has a brand new Thermalrake Smart 500w psu
I tried using HDMI and dvi to HDMI converter to no avail
Integrated graphics works fine w/o card. not when card is in pci-e slot though
I used 6+2 connecter to connect to 6 pin connector on gpu. With the extra pins to the side of course.
I am using the lastest drivers and GeForce experience for the 745 which is also comparable with the 660

I've installed many GPUs over the years and they usually show display right away just in low res until I install the required drivers. I'm stumped, fans spin, green light on the board is on.

Thanks a million for the reply as well