Memory problem with Asrock 4CoreDual-SATA2 R2.0 after oc

Just got 4CoreDual-SATA2 R2.0 a few days ago. Tried to oc it. when I inscrease the FSB to 280MHZ, the bios will only post my memory as a single channel, 1024 mb. Also in bios, it shows I only have a 1gb memory in slot 1. However, my cupz shows my system memory as 2048 mb, dual channel. When I lower the FSB, it would not recongize my second memory, unless I set my bios back to default , shut down my pc for a while and power it back. So what is the issue? Because I have a bad memory slot or FSB was too high for my motherboard.

Thanks for any replies.

Here is my bios spec:

CPU Configuration

CPU Host Frequency [Manual]
Actual Frequency (MHz) [280]
PCIE Clock [100MHz]
AGP/PCI Clock [66/33MHz]
Spread Spectrum [Disable]
Boot Failure Guard [Enabled]
Ratio Actual Value 13
Ratio CMOS Setting [13]
Max CPUID Value Limit [Disabled]
No-Execute Memory Protection [Disabled]

Chipset Configuration

DRAM Frequency [266MHz (DDRII533) ]
Flexibility Option [Enable]
DRAM CAS# Latency [5]
DRAM Bank Interleave [Auto]
Precharge to Active (Trp) [5]
Active to Precharge (Tras) [15]
Active to CMD (Trcd) [5]
REF to ACT/REF to REF (Trfc) [Auto]
ACT (0) to ACT (1) (Trrd) [Auto]
Read to Precharge (Trtp) [Auto]
Write to Read CMD (Twtr) [Auto]
Write Recovery Time (Twr) [Auto]
DRAM Bus Selection [Dual Channel]
DRAM Command Rate [2T Command]

→ Advanced Memory Configuration [Untouched]

DRAM Drv DQS [Auto]
DRAM Drv CS [Auto]
DRAM Drv DCLKA,B [Auto]
DCLK Output Duty Ctrl [Auto]

CLKBUF BUFIN_A Skew [Auto]
CLKBUF FAOUT Skew [Auto]
CLKBUF BUFIN_B Skew [Auto]
CLKBUF FBOUT Skew [Auto]

→ Advanced Host Configuration

Pipeline DRQCTL [Enabled]
GTL Control [Auto]

DRAM Voltage [High]
AGP Voltage [High]

Primary Graphics Adaptor [AGP]
AGP Mode [8x]
AGP Fast Write [Enabled]
AGP Aperture Size [256MB]
AGP Staggered Delay [Auto]
AGP GADSTB Output Delay [Auto]
AGP 3.0 Calibration [Auto]
AGP 3.0 DBI Function [Auto]
DBI Output for AGP Trans. [Auto]
DBI Output for FRAME Trans. [Auto]

V-Link Speed [Fast]
V-Link Auto-Disconnect [Enabled]

PCI Delay Transaction [Enabled]
IDE Drive Strength [High]
PCIE Downstream Pipeline [Auto]
OnBoard LAN [Enabled]
OnBoard HD Audio [Disabled]
Front Panel [Enabled]
CD-In [Enabled]
Bus No. [Enabled]
Echo TPR Disable [Auto]

My pc spec:
CPU: Intel E5300 2.6 GHZ
Memory: 2x Corsair VS1GB667D2 PC2-5300 1GB 5-5-5-15 240pin DIMM
HDD: Seagate 200gb
Vedio: ATI Radeon x1650 pro 512 mb AGP