Bueno, pues he instalado la última versión de la bios la v2002 y crash, no funciona. He vuelto a la anterior y luego he instlado la v1501, que si funciona pero no ha solucionado nada xD
He subido voltage de ram y NB y nada.
Total que después de estar toda la puta tarde con el ordenador he configurado la ram de la siguiente manera:
AI Overclock tuner: AUTO
CPU Ratio Setting: AUTO
FSB Frequency: AUTO
PCI-E Frequency: AUTO
FSB Strap to North Bridge: AUTO
DRAM Frequency: 800
DRAM CLK Skew on Channel A1: AUTO
DRAM CLK Skew on Channel A2: AUTO
DRAM CLK Skew on Channel B1: AUTO
DRAM CLK Skew on Channel B2: AUTO
1st Information:
CAS# Latency: 5
DRAM RAS# to CAS# Delay: 5
DRAM RAS# Precharge: 5
DRAM RAS# Activate to Precharge: 18
RAS# to RAS# Delay : 4
Row Refresh Cycle Time: 65
Read to Precharge Time: 4
2nd Information :
READ to WRITE Delay (S/D): 9
Write to Read Delay (S): 4
WRITE to READ Delay (D): 6
READ to READ Delay (S): 5
READ to READ Delay (D): 7
WRITE to WRITE Delay (S): 5
WRITE to WRITE Delay (D): 7
3rd Information :
WRITE to PRE Delay: 15
READ to PRE Delay: 6
PRE to PRE Delay: 2
ALL PRE to ACT Delay: 7
ALL PRE to REF Delay: 7
DRAM Static Read Control: Disabled
DRAM Read Training: Disabled
MEM. OC Charger: Enabled
AI Clock Twister: Light or Lightest
AI Transaction Booster: Manual
Common Performance Level: 12
All Pull-Ins: Disabled
CPU Voltage: AUTO
CPU GTL Voltage Reference (0/2): AUTO
CPU GTL Voltage Reference (1/3): AUTO
CPU PLL Voltage: AUTO
FSB Termination Voltage: AUTO
DRAM Voltage: 2.1v
NB Voltage: 1.38
NB GTL Reference: AUTO
SBridge Voltage: AUTO
PCIE SATA Voltage: AUTO
Y voilà! Funcionando a la perfección, ya tengo los 8 GB 
