K7S5A Restarting Constantly....PSU?

Hey guys, i hope someone will know the answer to my question and be willin to reply My current setup is;
CPU - AMD Athlon 2100XP
Motherboard - ECS K7S5A (Recommended by THG )
3D Card - Geforce 3 Ti 500 Verto 64MB
Hard Drive - 40gig 5400RPM Seagate
Ram - 256MB SD PC 133 (Branded)
Power Supply - 400watts
I have this anoying problem where-by the motherboard sometimes wont startup just keeps restarting in a continuous loop for about 30seconds, sometimes more. Then suddenly it will boot..strange huh? I have had this motherboard before and its done this. I figured it was a faulty motehrboard but obviously it isn't. I have tried creating a partition using fdisk to create a partition but when i did this the writing was all screwed up. Bits of the writing looked as though someone had tossed it randomly. After this the computer locked up and had to restart.
If i run the motherboard at a 100/100 (1500) CPU Frequency, the comp isn't stable, but more so than at 133/133 (2100). I was able to install Win XP Pro at 1500, but not at 2100 and still get the rebooting problem at 1500.
My friend has the same motherboard running the 2000XP chip and it does the same thing. I would be grateful for any replies...
Gazz

but i have tried 3 different types of ram (SD) both branded and unbranded. Its not the ram, has to be something else. Im stuck for ideas only thing i can think of is the PSU

Overclocking isn't Illegal!

The motherboard require high quality PSU and RAM.