Dell Optiplex 780 PCIe x16 Slot

What graphics are are you trying to use?

some dell boards have a limited slot wattage like here its limited to 25w and most cards need more to power them

http://en.community.dell.com/support-forums/desktop/f/3515/t/19657233

then on top of that that dell bios may not support just any cards and may be limited on what cards will work or not

some models of store bought computers [dell.hp,acer,ect..] may come with a ''locked or fixed'' / legacy or uefi bios and may not allow you to change certain hardware as a video card.. this is done to protect them from undue warranty claims and refunds .this is not done to hurt you but to protect them. you really need to see if that upgrade has been proven to work in your model first before you invest money in it .. there are a lot of these threads here at toms to look at some models will allow upgrades and some dont.. and a lot of guys here say ya ya ya when is really no no no...it would be sad you spent $200 on a card that won't post after you installed it as most find out. then get told its your psu and you spend more and end up right back where you are now, but its up to you good luck..


you got to know the boards in these computers are not like the ones we use to do custom builds witch are open to upgrading with in the boards compatibly . the bios is custom made for there design and just for the parts they authorize to be used on there computers there only guaranteed to work as is out of the box as you bought it ,..


also these boards do not have to meet atx standards and there pci-e slot power may not do the required 75w needed for most higher end cards and can be limited to say 45 or 60w that is all thats needed with the low end factory oem cards that it may of shipped with
[example]
http://en.community.dell.com/cfs-file/__key/communityserver-discussions-components-files/3514/1030.DESKTOP.jpg

in the end any upgrade you do is all your own risk . the prebuilt manufactures only guarantees there computers work as sold to you as is out of the box from there factory with what they put on it , not a drop more

there in business to sell you whole ready to go computers , and dont worry about you upgrading them or giving you support to do so . thats not how they make there money they prefer you run to wal-mart and buy there ''better'' latest models

with the 4650's dell offers only the 780 ''DT '' in in the Compatibility lists ?? may mean nothing but ???

http://accessories.us.dell.com/sna/products/PC_Gaming/productdetail.aspx?c=ca&l=en&s=niso&cs=caniso1&sku=A3055251&mfgpid=221049

http://accessories.dell.com/sna/productdetail.aspx?c=us&l=en&s=gen&sku=A2829980&mfgpid=201428

this one here shows for • Optiplex 780 DT • Optiplex 780 SFF


http://accessories.dell.com/sna/productdetail.aspx?c=us&l=en&s=gen&sku=A2829980&mfgpid=201428

those are low profile low watt cards and may be at or below 25w to power them and be used in that motherboards 25w limited slot

Since the cards you linked are older cards and don't have AUX power connectors they should meet the power requirements of the PCIe slot (75W). The only other thing I would try is to pick up a bigger power supply that is compatible with your system to test.

It could be that those cards are just incompatible.

Boot to "Safe Mode with Internet" and see if you get a display. Them remove the old GPU drivers and install the ones for the new card. Some of the newer computers have the low power GPU limit but I don't think the 780 did.