P5W DH DEluxe and E8400 &4890 problem- help requested

I updated the BIOS on my P5WDH to the latest available (2901) using the AMI afudos utility, and the system was working fine and stable.

A day later I intalled a new cpu ( E4800) and a saphire 4890 GPU. I did not upgrade the memory ( 4X512 high performance mushkin - for the time being) I was able to boot the system after reinstalling the CPU and the system ran for 5 hours in which I was able to install the new drivers for the 4890. An hour or so later the system froze and now keeps rebooting itself. The BIOS set up shows the temperatures as normal (40-50 C), the right speed (333X9) and I reset everything to default just to make sure there were no unusual settings. Still not stable. Any ideas of whjat I can try before giving up and reverting to my old config?

ATI Radeon™ HD 4890 - System Requirements

500 Watt or greater power supply with two 75W 6-pin PCI Express® power connectors recommended (600 Watt and four 6-pin connectors for ATI CrossFireX™ technology in dual mode)

[quotemsg=1834796,4,464242]- The power supply is an Enermax D 600W EG701AX-VE Noisetaker , mounted on an Antec D P180 Case


PS - last time I checked the BIOS was still reporting the right processor type and frequency but had the FSB at 1333, - Multiplier remains at 9. THe ASUS support website says:
:"Due to chipset limitation, i975X chipset is not able to support all the features of 45nm CPU. The following is a list of the limitations:
1. VT function does not work.
2. The maximum FSB is capped at 1066MHz.
3. 0.5 CPU multiplier is not supported.
4. L2 cache size is not recognized correctly. However L2 cache is still functioning."[/quotem

UPDATE

I have been able to get stability ( so far) by underclocking the CPU to 2.4 to match the maximum FSB cap at 1066MHz ( According to ASUS- see point 2 above). I am beginning to test increasing the CPU frequency by .1 at the time to see how far I can take it. ( This is the first time I have tried to change frequencies). All I know so far is that it is not stable at FSB=1333 Mhz ( CPU at 3.0, its rated frequency) and it appears stable at FSB=1066 (CPU at 2.4)

I assume the 1066 cap is based on an average and different instances of the same board can be overclocked to different thresholds. Mine is fine at CPU=2.8 which is close enough for me. Plan to upgrade the board eventually.