|You do NOT have to disconnect the 24-pin main ATX plug from the motherboard. Just make sure that the power cord is unplugged from the wall, then move the jumper from pins 1-2 to pins 2-3, wait a few seconds (not minutes), then move the jumper back to pins 1-2 again. Plug in the power cord, boot up, enter the BIOS & correct the settings. And don't attempt to overclock again until you learn how. Changing the RAM timings really isn't overclocking anyway & from the looks of your RAM description, you're not running dual channel mode.|
"i have dual channels one channel is 1 gb ddr2 and the second is 2 gb ddr2"
Dual channel is a function of the board, not the RAM...to enable it, you need to have the correct RAM (matched pair) installed in the correct slots. If you have a single 1GB + 1 single 2GB, you're probably not running in dual channel mode. You would need 2 x 512MB + 2 x 1GB to be able to run 3GB in dual channel.
Post your complete specs...motherboard make/model, which Core 2 you have, which DDR2 RAM (533, 667, 800, etc), which video card, power supply etc. If you wanna overclock, I can suggest some settings.