I put the CD in and boot the machine. The initial Ubuntu screen comes up ("Ubuntu" with the line of dots below it) for a few seconds, and then it disappears and I see this text: initramfs , so that i couldn't do further. please help to solve this problem thank you
When having this type of problem booting a CD my advice is to check the integrity.
As you boot, select the "Check disk for defects"
The boos screen looks something like this
You may also want to check the iso you downloaded. See Ubuntu Wiki MD5SUM for details.
I just had this problem with my Ubuntu 11.10 live DVD. My problem was fixed by changing the SATA settings in the bios. It varies from computer to computer by most likely just switching to the other option should fix it. For example I changed mine from IDE to achi. It worked like a charm. If you need more detailed instructions could you provide your motherboard make and model.