Basically I get the exact same problem as this person :
But this was a while ago around version 13. I've done the nomodeset xforcevesa thing. No dice. What is really strange is that I already have regular Linux Mint 15 installed which works perfectly. What amuses me even more is that I had the same setup with an old geforce gt 220 and everything worked fine with quadruple boot grub (like I always do, it might have become a three boot machine as I am now experienced enough with Debian to just use LMDE). I can give my whole specs if that mean anything.
AMD Athlon II X4 645
Corsair Vengeance 8,00GB Dual-Channel DDR3 @ 800MHz
ASUSTeK Computer INC. M4A78LT-M-LE (AM3)
2048MB ATI AMD Radeon HD 7800 Series (Sapphire/PCPartner) (7850)
It also has an onboard video card but all operating systems do not even see it when I have my 7850 connected to a monitor. I don't know if I can disable it in the BIOS, but considering everything works fine in regular Linux Mint...I'm perplexed as to what is wrong here.