msi nx7800gt no composite output/256colour output on svhs?

Hi,

For some reason i can no longer output in composite video its blank,also when i change to svhs the definitition of the picture is fine but it seems to be stuck in 256colours no matter what i do.

the only thing i can think of is the tv output chip its self has been damaged in some way or a diode or capacitor has blown

also in the nview display no matter whether the tv is plugged in, it still gives the option to use it.

thanks