I have just replaced a single 1G ddr2 667 ram with two identical 2GDDR2 667ram but unable to boot. message appear stating " ddr2 ram 667(single channel)" How do I solve this problem? thanks

1st of all, your motherboard has to support dual channel mode. 2nd, you have to install the RAM in the correct slots. If your board only has two slots, it's a no-brainer, but if it's four, you need to know which two to use. Check your motherboard manual.

In addition to the above information, if the computer goes that far the problem isn't single or dual channel. If the computer ran OK before swapping out RAM then either the new RAM is incompatible with your motherboard, or you may have disturbed something inside the case. The memory settings in the BIOS may be wrong, causing the no boot. Reset all cables, RAM and cards. Have the computer unplugged when performing any changes inside and exercise proper anti-static precautions.