IMac with Snow Leopard doesn t work without second display connected
I've a iMac 24" and I would like to resell it urgently.
But I've a big problem, if I disconnect my second display (belinea 20"), the iMac screen become grey or blue after many second.
If I boot system, after the grey clock : nothing, grey or black screen.
The Os is snow leopard disc, update version (10.6)
The iMac version is iMa8,1
The EFI bios is : IM81.00c1.b00
I tried :
Reinstall with format
Utility disc on boot cd (scan disk & rights repair)
Even when I try to boot cd without second screen, I ve white screen
(after a update to 10.6.4)
Help me please
MacPro4,1, HD4870