What size are your protein markers? Remember that a thicker gel works best for larger molecules. Did you boil the protein ladder to denature? If someone else made the reagents, make them again yourself.
Hello Moumita. As Katie indicated - check your markers. You may be using a set of low molecular weight markers. If you are in doubt, load 1 ug of BSA (67-kDa), run the gel, and stain with Coomassie.