Help - 8600GT Graphics bringing down system

I just bought a new graphics card Gigabyte 8600GT (gv-nx86t256d) for my system as a stop gap till I upgrade.

However this card seems to bringing down the entire system. Problem and details as follows.

MB: MSI MS-7100 Diamond (old socket 939 board)
CPU: AMD 3800+ X2
OS: Vista Ultimate x86
RAM: G-Skill ZX 2Gb
PSU: 700W SLI ready
Drivers: Graphics & Nforce4 - Native Nvidia (latest) rest MS
GPU OLD: nvidia 6600 - all works good
GPU NEW: nvidia 8600 - system freezes solid
BIOS: ver 1.0a

Problem:

On system boot sometimes BIOS only reports single core instead
System will boot but locks when processor put to work
Sometimes bios will report 2 CPU's on boot but will continue
to hang anyway once processor put to work


Question:

Has anybody else got this board with this card and all good
Has anybody got a clue as to what is going on please

Help appreciated.

Are you using both the old and new card ?

No only one at a time

Never mind I finally fixed it myself. It seems that for some reason the bios kept dropping the CPU Core voltage to the lower level that is acceptable for the type of CPU. I manually corrected it to the maximum allowable and alls well that ends well.