arcadevga and a scart tv

[nnndoh]

i need input

I've build my own vga to scart cable ( very happy it works ) but autoswitch to AV doesn't work
when i connect the tv and computer monitor to the arcadevga, i see a boot screen on my computer monitor

then when i extend my desktop to my tv, i see a clear sharp image at every resolution



but, when i restart my computer with only the tv connected at the 15 pins connection
i see a sharp clear image of my boot screen, the windows is loading animation.


but then i see this...




what would cause this?
at first, resolution was set at 640 x 288.. what  weird is, if i want to choose another frequency, i see only a blank field.
would it solve the problem if i install windows xp instead of windows 7  64 bit?

[nnndoh]

problem solved, downloaded 64 bit drivers from ultimarc