Ok, baholete, firstly, thanks for filling in those specs - 'crap system 9000' is a nice touch.
I don't blame you.
From your latest description, it's beginning to sound like your original graphics card is bad for sure and your mobo likely. Your PSU is very likely causing funnies too, judging by that 8800GTS working fine. It could also be an issue with the mobo BIOS... see what I mean about endless possibilities?! lol
The thing to do now, is to beg, borrow or steal a
decent* branded PSU (420W or higher) from a friend and see if those three graphics cards start up normally. It really wouldn't surprise me if you have three duff components there, my friend; it does happen unfortunately. Heck, you could throw in your original card, now confirmed bad... bet it works fine just to have you tearing your hair out!
The other thing you need to do, is to have the barest minimum connected to make the system boot and give you a picture ie only CPU, mobo,
one** stick of RAM and graphics card. Unplug literally
everything else, including the mouse. This eliminates the possibility of a duff component screwing with your mobo and confusing it. Heck, you can even remove the keyboard, but then you obviously can't control the PC. Again, there's too many fine details to try, so can't go into all the possibilities here and is the sort of thing that becomes apparent to one as your fiddling with the system.
Another thing to do is to clear the CMOS RAM, as in removing the battery, using the clear jumper and loading defaults. This one's quite important to do (and don't forget to put the battery back!) Also, if you have any other jumpers on that board, set them to their safest or default positions. I would like to recommend you flash your BIOS to the latest version too, but your system is too flaky for that right now and a bad flash will brick it instead, so don't do it. You may want to consider it if the system is running stable with that spare PSU though, but please run it past us first.
At the risk of you having answered this earlier, your system isn't overclocked right now is it? Everything must be running at stock speed for troubleshooting.
*Corsair, Enermax etc (not so keen on Antec anymore; tend to have problems, from experience and forums)
**You can try swapping sticks if system still acting weird