A8N SLi Deluxe with ATI 2900 Pro power alarm (?)

[Maviso]

Asus A8N SLi Deluxe - new Xilence 700W
Upgrading video from Asus EN7600 GS to Sapphire ATI 2900 PRO 512Mb - works fine except in full screen mode.
Uninstalled all NVidia graphics drivers via control panel and EN7600 via device manager.
Connected card to motherboard & used 2 x 6 pin PCI-E power cables for Xilence 700W ATX 12v V2.2 power supply.
Installed Sapphire card using installation disc. Updated drivers from ATI to 7-10_xp32_dd_ccc_wdm_enu_53250.exe
Card works just fine until you run anything (ie game) in full screen mode at which point the card alarm sounds continuously to indicate a power supply problem. Come out of full screenmode & everything works just fine.
I have also connected the EZ-Plug to the motherboard without effect.
If I install the same card in my Asus A8N32-SLI Deluxe board (similar peripherals spec but only 480W Xilence power supply) the card runs everything you care to throw at it full screen or otherwise.
I have tried eliminating the power supply by swapping the 480W from the A8N32-SLI Deluxe board into my machine but still the same problem. I have re-set the BIOS to factory defaults but still the same problem. There is no overclocking or overclocking utilities working here. Help!

 

[o1die]

I would disable the alarm if this is from a saphire software program or asus probe. Many alarms are false. Asus probe is nortoriously sensitive to power supply readings.

 

[Maviso]

The alarm is built into the Sapphire graphics card itself so not really an Asus probe or alarm. I'm a bit concerned about frying the card as I don't know if the alarm is (erroneously?) signalling over or under voltage or lack of amps.

It has been suggested that I try the card in the other SLi slot but I understood that using just a single card in the second slot worked with less performance.