No pc display !

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So I got this very ancient hp pc with 1 go of ram and no gpu (obviously) and no hdmi support , the only way to display something is with VGA cable plugged directly to the motherboard , it worked on old monitors but when I plug it with a tv ( an old one ) it displays booting options and all that stuff , like it would normally do , but as soon as windows start up , black screen , the tv displays " no connection " .
The windows installed is windows 7 .
Does anyone have any ideas how I can fix it ?