http://forumz.tomshardware.com/hardware/Core2Duo-Overclocking-Guide-v1-ftopict197995.html
1. Disable ‘AI Tuning’ for ASUS, ‘C.I.A.2’ for Gigabyte
2. Set PCI Express (PCIe) frequency @100Mhz (‘Auto’ for DS3/DS4/DQ6)
3. Set PCI frequency @33Mhz
4. Disable Hyperpath 3 (for P5W DH only)
5. Disable any ‘spread spectrum’
6. Disable Q-Fan (for ASUS only)
7. Disable ‘Limit CPUID Max to 3’
8. Disable any overvoltage protection
9. Disable ‘C1E’
10. Disable ‘EIST’
11. Disable Virtualization Technology
12. Disable No-Execute Memory Protect
13. Disable any other thing you don’t use
14. Do not enable any speed enhancements you see
Try some of that, also make sure timings are entered correctly for RAM and make sure you use small enough intervals in your step ups, I did 3 mhz on the FSB each increase.
Also MAKE SURE YOUR BIOS IS UPDATED. Mine wasn't when I bought it, that should help a lot, when you boot up it should say. It should be F6, it should be under mainboard in cpuz also.
Male sure you take the time to stress test.