Grub is not coming (screen remains black!) and other grub issues [Ubuntu 12.04]

Problem:-  Sometimes after installing Ubuntu along with any other OS makes grub invisible,rather a black screen.

Solution:-  This problem occurs due to low resolution of your graphics (or monitor).This can be solved via terminal.
Open the terminal by pressing ctrl+Alt+T

Now type in the terminal the following command:-

sudo vi /boot/grub/grub.cfg

Then a 'sudo' password is wanted,give your password there.
Now find out the line

"set gfxmode=" [It may be 'set gfxmode=auto' there]

Now put set gfxmode=640*480
And put the following line underneath it

 set gfxpayload=keep

That is it will look like

set gfxmode=640*480

set gfxpayload=keep

Now reboot and see that the grub is coming or not!

Many times this process becomes useless,then keep intact the grub.cfg to its initial form and follow the following process

sudo gedit /etc/default/grub

Now uncomment the line #GRUB_GFXMODE=640x480 by removing # ,then save and quit gedit.And now type

sudo update-grub

and reboot.
If grub menu still does not come then comment out the line in the same file written just above GRUB_HIDDEN_TIMEOUT=0 by putting a # before it,save and quit.
And type in terminal

sudo update-grub

and reboot.