Help with a poorly X5DA8 please...

Hi,

I have a X5DA8, and the POST when you power it up is one long continuous beep or siren...

I have reseated the CPU's with new Artic Silver 5, tried with just one CPU, I have also checked the auxilliary rail J15 is supplying 12v...

I have 4 x Corsair PC-2100 256MB Registered DDR's present...

Does anyone have any ideas where the fault may lie, or any further troubleshooting procedures for me?

Thanks in advance,

Susan