Dimension C521 video problem

My Dimension C521 stopped sending video signal to the external card. When I try to use the onboard, send a green signal.
Everything works fine but the color green predominates.

What could be the problem?

Moterboard is broken, external card is broken, any idea what should I do?

I Need to know if the following models of motherboards are compatible with my Dimension C521.

HK980
UW457
CT107

I use the procesor AMD Athlon 64 X2 Dual-core.

if exist other compatible model of motherboard, please tell me.

Sorry for my english.

best regards