Hum aqui diz que suporta x16 embora esteja selecionado x4 não tou a ver onde mudar isso mas prontos. Nem na bios nem nas propriedades da gráfica.
Display adapter information
$ffffffffff ----------------------------------------------------------------
$0000000000 Description : Radeon X1600 Series
$0000000001 Vendor ID : 1002 (ATI)
$0000000002 Device ID : 71c2
$0000000003 Location : bus 2, device 0, function 0
$0000000004 Bus type : PCIE
$000000000f PCIE link width : 16x supported, 4x selected
$0000000009 Base address 0 : c0000000 (memory range)
$000000000a Base address 1 : none
$000000000b Base address 2 : ff4f0000 (memory range)
$000000000c Base address 3 : none
$000000000d Base address 4 : 0000c000 (I/O range)
$000000000e Base address 5 : none
$ffffffffff ----------------------------------------------------------------
$ffffffffff ATI specific display adapter information
$ffffffffff ----------------------------------------------------------------
$0900000000 Graphics core : RV530 (4tmu)
$0900000002 Memory bus : 128-bit
$0900000001 Memory type : DDR2 SGRAM
$0900000003 Memory amount : 512MB
$0900000004 Core clock : 499.500MHz
$0900000005 Memory clock : 391.500MHz (783.000MHz effective)
$0900000006 Reference clock : 27.000MHz