Possible Duplicate:
What is the difference between 32-bit and 64-bit and which should I choose?
when i try to run the machine a messeage appear in the black screen sayinh "this kernel requires an x86-64 CPU, buy only detected in a i686 CPU. Unable to boot please use a kernel appropiate for your CPU"
i'll aprecciate
Check some possible reasons:
This is happening because you are trying to run the 64-bit version of Ubuntu on a 32-bit machine. You are probably attempting to boot from a live CD/DVD or live USB flash drive. If so, you'll need to download the correct ISO image (the one with i386 rather than amd64 in its name), and burn a new CD/DVD or write the new image to the USB flash drive.
If this is happening on an installed system, that's somewhat strange. As Beernarrd has said, it's possible that you are trying to boot an Ubuntu system from a hard drive that was moved to a 32-bit machine from a 64-bit machine. It's also possible you've replaced your 64-bit CPU with a 32-bit CPU, but that's also pretty unlikely--these days, there aren't that many motherboards that take both 32-bit and 64-bit CPU's. (Also, if you had just replaced your CPU, you would probably have told us about that in your question...)
I don't think it's particularly plausible that this could be caused by GRUB pointing to the wrong kernel. 64-bit kernels are extremely unlikely to be installed on a 32-bit system. If you had done that, you would probably know about it. It's not the sort of thing you can usually do by accident.
To reiterate: If this is happening when you're trying to use a live CD/DVD/USB, the problem is that your machine has a 32-bit processor but you used the 64-bit .iso image (with amd64 in its name) rather than the 32-bit .iso image (with i386 in its name).
