ECS kt600-A incorrect cpu frequency

Hi
I have a Socket 462 Sempron 2500+,ECS KT600-A, corsair VS512MB400 pc3200 ddr memory, bios 1.2c (most recent), antec 350W power supply.
the motherboard frequency jumpers are set at 100 Mhz. If I set it at 133, the system freezes. If I set it at 166, which is the correct setting for this processor, the system won't boot. The ram is a single stick of 512 MB double sided and the Corsair website says it is compatible with this system. In the Bios, the FSB is shown at 100, the DRAM freq is set at 133 by SPD, CAS Latency 2.5. When I turn the computer on, the POST screen shows the processor to be Athlon XP 1050 Mhz even though this is a Sempron 2500+ retail boxed cpu. I have tried changing the cpu and dram frequencies in the BIOS also, but the system again becomes unstable. This has been this way since I bought the system. Any ideas how to get the system running correctly?
thanks.