ECS L7VTA + AthlonXP 2000+ problem

I've already bought an ECS product : L7VTA motherboard with an AthlonXP
2000+ processor.

But I have a little problem with my computer.
When I benchmarked my computer, I always get a different result.
I'm using Sisoft Sandra 2003 to benchmark my computer, using CPU Arithmetic
Benchmark and CPU Multimedia Benchmark test.

When I am turning my computer on, and benchmarked it, I get a good result as
well.
But, if I restart WindowsXP, and do the benchmark again, the result is
different from the first one. The result is so poor that my processor Athlon
XP 2000+ is running more less like an Athlon 1 Ghz. It happen also when I go
into bios setup, and the computer goes to restart again.
So the problem is, when I restart Windows or booting my computer (warm
boot), the processor goes into a low performance. But in the initial screen
when booting, it is shows that the processor is running as Athlon XP 2000+.

It happen also with 3DMark2001SE scores, when the processor goes to low
performance, the result is also lower.

I've set my processor to run in normal mode (not overclocked), with 133 FSB
and DRAM setting at 133 also. I am using a Geforce 2MX400 and DDR2100 128 MB
memory.

I would like to ask if anybody could give me a technical assistant, what wrong
with my computer?
Beside that poor performance, I did not encounter any stability problems.
My software goes well, but it runs in poor performance.


My computer specification :
AMD Athlon XP 2000+
L7VTA rev 1.0
128MB DDR266 V-gen CL2.5
Seagate Barracuda 40GB
GeForce 2MX400
Windowx XP Professional