GA-K8N51GMF overclocking. need help...

First of all, here are my specs so that everyone would know why I'm starting to hate this motherboard:

Processor: Sempron 2600+
Motherboard: GA-K8N51GMF (sux!)
Memory: Kingmax Super Ram 2x256 PC3200 (2.5-3-3-7@133mhz)<---timings
Video Card: GeForce 6600GT 256Mb/128bit PCI-Express
Power Supply: Task 450W
Heatsink for Processor: Thermaltake Big Typhoon (modded fan to Koala)

Now, down to the dirty stuff. I tried to set the multiplier of the ram to 133mhz to set the FSB to 250. I attained 2.0Ghz from the stock speed of 1.6Ghz. Everything was good and tried stress testing with OCCT and my temps were great. So I thought I was getting a good OC and I was happy. After stress testing I tried palying a game, then what do you know, it restarted. It was only a matter of time and I was tired of the frequent restarts when playing a game (Tantra Online, NFSMW). Why is gigabyte limitng their motherboards nowadays. Can anyone help me get a stable OC @ 2.0Ghz? What do i need to do?