Looking briefly @ your mobo specs, you could try to go stock/retail

I see that your p5b has a JMicron HD controller which used to cause errors, but if you're all SATA, give it a go.

You can find a guide over @ insanelymac that worked for many P5 series, under step 4 you'll find my guide too.

I can only verify things for p5q-em, but the procedure is the same, just hunt down the necessary drivers and give it a try.

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Most people are so lazy, they don't even exercise good judgement!

Hack: Asus P5Q-EM, Intel Q6600, Crucial 8GB DDR2, nVIDIA 8800GT/512MB, Optiarc AD-7200S, A few HDs (All SATA), X.5.7 Retail

Into it just for the fun of it...