It's not clear from the above whether you tried to attach the monitor to the on-board DVI -D connector or if you put the Graphics card back in.I pulled out my graphics card entirely and the PC turns on. Someone suggested messing with the BIOS settings but when I attack my monitor nothing displays so i cant get to the BIOS settings because my PC doesn't recognize the card. So im closer but still need help if anyone can assist.
If you can, try to remove everything except the CPU (+fan), RAM and the PSU. Then boot with the monitor attached to the on-board graphics adapter. If that works, then add mouse and keyboard and see if you can enter Bios setup. Make the appropiate changes and shutdown. Then insert other parts one at a time, rebooting between each part. Once and if you reach a no booting status, then you've found the culprit.
BTW: are all the front connectors attached - if they are present in the case - such as HDD Led, Reset, Power Switch, Power Led? disconnect all but the Power Switch. Then, as before, connect one at a time and make sure it boots every time.
EDIT: I forgot to ask if there's any beeping when you try to turn it on?