If you set the external clock to 233Mhz that is a 563Mhz overclock on the CPU, unless you used a lower multiplier and a 33Mhz OC on the memory, unless you used a ratio besides ddr400.
Give the CPU and memory more voltage or back off on the OC.
You should also lower HTT/LDT multiplier/ratio if you are overclocking. Stock is 1000MHz, or 5x, drop it to the 3x, or 4x multiplier (sometimes listed as 600 or 800Mhz).