Try this 1
First make sure that you have properly placed the RAM back into the slot.
If you notice that your CPU fan is running but there is no display in the screen,
then remove the RAM from the slot, clean it and place it back properly or try
If you have no idea about RAM, then click on the below hyperlinks "Images".
Removing a RAM
Check your RAM also. Even bad RAM will result in display problem.
If you are having two RAMs then remove it, place only one RAM and check the
display. If you failed to get any display then change the slot. If you still failed to
get the display then try the above procedure with the other RAM.