Bad polymerization, bad buffer, overloading gel as a start.  Try running molecular weight markers and known proteins to trouble shoot. 

It looks like bad polymerization to me, perhaps in the stacking gel?

 Hi Maria,

I would check the buffer that you used to cast and to run that gel. It reminds me of a time when a student in my lab used TBE meant for DNA gels to either cast or run his SDS-PAGE gel.

Ciao Maria,

 I saw that when the polymerization of the gel didn't occurr properly...Where markers are? Is it the voltage high?

Ciao

Hi Maria Teresa,

    I saw yr picture, I thing this gel didnt  have polymerisation. One thing, u should properly maintain the pH both staking and seperating gel buffer.

second one is, the voltage is very important for SDS-PAGE, First u wil give 80 V for staking and  then give 100V for seperating buffer.

Next, sample concentration doesnt exit 50 microgram.

U will try tis protocal. Al the best

Radhiga Sundaresan.