Yesterday it was working fine and today it is not
I imported my obj file and it is not showing up or it is too small I guess but I can see it on outliner.
It could also be way to big, try hitting the . key on the number pad and see where it takes you, if it's to big, scale it down. It also helps to set the origin to "centre of mass" or "geometry" and resetting its location with alt+g.
Your question provides very little information, so it's just guesswork here. I assume you exported your OBJ again. Check your export settings, especially the unit setting in your export programm. Try setting blender to the same unit used as in your export (under 'scene properties').