video graphic error

i dont understand why my hp dv2731tx notebook laptop cant recognize the updated nvdia video adapter... i already updated its bios and recognize it. it only runs on standard vga and everytime i installed the nvdia which is required i t create a horrible screen.. i also check the resolution and i found out that it was only running on 4bit... and it was happened if the nvdia was insytalled. my os now is vista ultimate because my current os which is included on the package when i bought this laptop was already corrupted..even the recovery disk was not working anymore.. pls help.. thanks a lot!!!!