I am trying to boot a live Ubuntu iso file from my thumb drive,usin the tool,Unet Bootin. it all goes well till the booting process. but once the booting starts it says hat the cd is missing and to try again by inserting the cd,it really annoys me could some one please help me out of this?
That's a strange error. I'd re-read the instructions for unetbootin and load ubuntu onto the stick again. If that doesn't work, try fedora or a different distribution to see if you can load into the system.
I played with unetbootin a month or two ago and it went smoothly for me, but I think its finicky about what is on the stick, so maybe cleaning out everything from the stick before trying again?
Did you try a different distribution other than ubuntu? Perhaps its a strange combination of hardware and software. Try Fedora, just for kicks to see if it works. If it does, load ubuntu again and try try again. If it still doesn't work, maybe an older version of ubuntu and after its installed you can update.