how to configure grub from a live CD
 

I have installed ubuntu 8.10 and grub is installed in MBR. I could run both ubuntu and windows after that, but I changed grub configuration from ubuntu.

because I wanted the other people on my family who use this computer to be easily able to go directly into windows, I changed the default os to windows and I wanted to set the delay time before loading the default os to the least possible, so I made that 0.

after that I can't boot into ubuntu. I thought it's possible to override the default by pressing a key before it comes to load grub, so, that key be pressed while grub is loaded and grub gets it, so I can load ubuntu. what can I do? from a live CD or anything else. Thanks.

The point of the "delay time", strangely enough, is to allow you to choose something from the grub menu. While the delay counts (it says something like "GRUB: booting default windows in 3 seconds) you can hit any key to get the menu. Or you can remove "hidden menu" and you will actually see the menu for three seconds.

But if the delay is 0 you can't.

reinstall grub from the Ubuntu Cd

or simply boot a live cd and edit /boot/grub/menu.lst as per above post (set delay to 30 secs )

I went through live CD and I changed menu.lst but it didn't work. I know if I changed menu.lst it must work because grub reads from it.

I changed timeout (delay time) to 10 and made the line that was saying (something about) "hiddenmenu" commented , to get not executed. Stranger than ever is that menu.lst contained no entry for windows.

It had some entries to open linux on first partition of the first hard drive, which is windows not ubuntu. I made some changes to have it point to linux drive either. I'm not sure if I was correct or not, but at least grub should show the menu, then let me choose of the wrong entries.

please tell me how to reinstall grub from ubuntu CD or to have it prepare some entries for itself, like it did when ubuntu was being installed.

If you open /boot/grub/menu.lst while using a Live CD, and depending on the Live CD you are using, that file either won't exist or it will be the menu.lst for the Live CD, not your Ubuntu on your HDD. Are you sure you edited the menu.lst in your Ubuntu install? How about doing:
And find which is your Ubuntu partition in the form sdaX (like sda5 for example), and then do:
But replace sdaX with the Ubuntu partition. Then you should get your Ubuntu menu.lst. How about giving that a shot and let me know how it goes.

It worked. Thank you very much.

You're welcome, glad that did the trick. Cheers and have fun with Ubuntu. :)