Asus P5gd1 Overclocking Problems

I'm new to the overclocking world but someone out there has to have simliar problems.I have a asus p5gd1 with p4 3.4 cpu and a new watercooling unit. I did have a large cpu fan which I could reach a steady 3.6 and no problems. More than that it became unstable, temps was around 100.00F-104F. I have the new thermal take big watercooling system. Basically problem is the cpu, I dont think its temp related but not certain. With fresh artic silver I could go as high as 3.85 mhz for 1 week. Then it started to lock up, I goto bios to look at cpu temps and they were always around 91f-100f no more. So I thought maybe cpu block wasnt tight. So I took cpu block off of cpu cleand and reappy artic silver, Its exactly 7 days I did that last friday and tonight it locks up. So I dropped the fsb down to 3.6 still locks up over time. Temps look ok in bios. It almost seems like the artic silver is getting dry then cpu gets hot or locks up. If I reapply artic silver I can overclock to 3.85 and run the **** out of it for 1 week than it gives me trouble. Please help dont know what to do.. Thanks Del