@ omagic
Thank you for your reply. I did change the power supply yesterday. I now have it on an Antec 500 watt power supply. No change in reboot issue. I will also try replacing the bios battery, since this motherboard was purchased about 5 or 6 years ago.
The memory is OCZ platinum 800 5-5-5-15 1GBx4 with increased voltage as per OCZ to 2.2v, 2 disks are 1TB mirrored, IDE DVD burner, well ventilated case, AMD stock fan with heat pipes. I have had the memory set at 4.0 and 3.33 multipliers. I can play around with the FSB and CPU multipliers in numerous combinations, but when the CPU frequency gets to 3.3 the soft reboot problem occurs.
You should also know that this motherboard had its own GPU (but I use a HD 5770)). The HT Link speed reported by CPU-Z is around 1000, likely for that reason.
@Dark Mantis
Yes, works fine at default settings and now overclock (with OCZ recommended extra voltage for 4 memory cards). Bios is 7Fi, which was cleared after installing new CPU.
I do also have another DDR2 system in which I may test CPU and memory overclocks for this CPU and Memory.
@ others
In searching the internet and futuremark, I have not found a person with this motherboard whose CPU frequency has exceeded 3.3. Does yours?