Start by listing the exact model of every part you bought.
No video is such a common symptom that there's no way it can be diagnosed accurately with such little information. I highly doubt it's an issue with your card requiring more power than your PSU is offering unless the PSU is faulty. You generally wouldn't see symptoms of that until you start playing a game or running a benchmark that will max out the card's thermal design power (TDP). Most high end cards these days have around 200-250w TDP, with the exception of a few outliers such as the 6990.
Here's a few things that can cause a computer to power on but not display video. They are in no particular order, and some of them are rare:
Bad power supply
Bent socket pins
Bad DIMM slot being occupied by working RAM
Bad video card
Bad video card port
Forgot to connect PSU 8-pin connector to board
Incorrectly seated RAM
Incorrectly seated video card
Motherboard limitations between memory controller and SATA ports (e.g., cheaper motherboards might disable 1 SATA port if all 4 DIMM slots are occupied)
clear CMOS jumper missing
Bad CMOS battery
Memory profile needs to be set in bios before occupying all four DIMM slots
Incompatible CPU (for example, an ivy bridge installed in a Z68 that needs a bios update)
Just to name a few.
You didn't mention if you have an internal speaker in your case, which would provide beep codes to help you diagnose the problem. I know you're still working outside the case but I recommend connecting that speaker anyway. If you do have the speaker connected and are not getting beeps, any of the above can still be true. Modern motherboards have LEDs that light up in a series during post to indicate which controllers/hardware is initializing. The LEDs will hang at a certain point and the mobo won't post, and you'll be able to see where it's gone wrong.
This post was edited on 11/22 at 10:24 am