Problems overclocking X2 3800+

Could someone perhaps give me a few tips with overclocking here? I've been through AnandTech's X2 overclocking guide and every other overclocking guide I can find, but I've had no luck at all.

I can push bus speed up to 210 no problem, no other adjustments needed. If I try 215 or higher, though, the system's disk LED stays on, and it reboots at the point in POST where it would detect the drives. I've tried everything suggested in the guide - lowering the HTT multiplier, lowering RAM speeds to 333 or lower, etc. No difference at all.

Hardware: Athlon 64 X2 3800+, Gigabyte GA-K8NF-9 motherboard (latest BIOS), Kingston DDR400 RAM (2 x 512MB), Gigabyte Geforce 6600GT graphics card, Maxtor 300GB SATA drive on SATA 0, Lite-On DVD writer, Lite-On combo drive, 400W power supply, adequate cooling (even at 100% utilisation, CPU temp is only around over 45C).

Any ideas? Something to do with SATA maybe?