I bought the HD3870 shows how 3800

This is demonstrated by the
ATI Radeon HD 3800 Series (RV670) 512 / Sapphire

that I bought the HD3870 is not?

either wrong or drive you absolutely had taken in 3800 is not 3870 ATI graphics card series are shown to your normal display.
I bought the HD4850, is shown in the HD 4800 Series is the 3870 general theory is driven by the 3800 drive system.Boot logo should be before the show.But this is not necessarily to associate.