Why did my AMD athlon 64 x2 3600+

[jonathonism]

I just bought a asus motherboard, went to overclock the cpu, had it running stable at 2.6Ghz first 36 to 48 hours then went to restart, upon windows loading it froze, I cant get it to load higher than 2.1Ghzx2 stable. With no changes to the BIOS How do I get back to 2.6Ghz. Any help greatly appritiated. Motherboard M2N68-AM Plus

 

[jonathonism]

I just bought a asus motherboard, went to overclock the cpu, had it running stable at 2.6Ghz first 36 to 48 hours then went to restart, upon windows loading it froze, I cant get it to load higher than 2.1Ghzx2 stable. With no changes to the BIOS How do I get back to 2.6Ghz. Any help greatly appritiated. Motherboard M2N68-AM Plus