Hey no probs man, what you also could do is save up more money so you can afford the better PSU< since if you have to sell that cheaper one in a few years you'd only be making loss as money goes, just want to give you the best advice, since it will save you money in the end.
As for the display issue, yeah I know this all too well, I had it too after I first slapped them together, I thought they both died on me :X So yeah, is a very well known issue, after redoing them with much more patience and care I succeeded and they both worked yaay, as that maintenance thread clearly shows rofl!
The DVI-I's are mounted on the Slave PCB, which is the PCB without the PCI-E 2.0 x16 connector, so if this part is disconnected from the Internal SLI conenctors, it won't give you an image, so this explains your exact problem
So thereby I too think that your Internal SLI ribbon cables have gotten loose.
Just make sure when you have connected then, very be as gentle as you can by remounting the HSF and everything, because one slight wrong move or jolt will loosen them again, this made me do the entire process for both cards twice
I kinda suck when it comes to such things, since my hands are extremely shakey to some certain point :X
Just telling you this, since they have a very complicated construction, lots of care and patience is required for you to succeed
