I would clear cmos for like 30 minutes. Sometimes it takes a while for those bios to reset. If you are plugging into mobo and graphics card and neither words, something is wrong in the bios assuming wires/monitor are good.
Ok so it was working before you took it out of the old case. And let me presume when you put it all in the new case it decided not to work.
Did you use an anti static wrist band when you did this as static can damage any of the parts in question.
Anyway the question is do you get one short beep from the motherboard to say everything checks out ok. If you do as I sure you should since the board is detecting there is no memory fitted have you.
1.Gone into the bios and set the Pci-e as the default graphics output device.
2.Disabled the on board graphics solution.
3.Double checked that the 8 pin 12v is connected, located next to the cpu socket, this also provides a bit of extra power to the Pci-e graphics slot from the board.
4. Connected any extra 12v pci-e power connector to the back of the graphics card in the pci-e slot if needed.