May be the concentration of the SDS is too high so that even the marker cannot be separated

You can prepare fresh gels. Make sure that you add the right amount of solutions or components that are needed to prepare the separating and stacking gels. You can prepare the gel 1 day before running the gel so that it polymerizes better. Also, you can make sure that you prepared the running buffer properly and add a sufficient amount of running buffer to the chamber. Good luck!

In my opinion, this is due to solution/buffer constituation/quality. I would propose to prepare fresh solution/buffers and repeat the procedure.