When you say ‘my mind’s gone blank‘ it means that suddenly you’ve completely forgotten what you were about to do or say.

For example:

Even though I’d been preparing for the interview for days, 

my mind went blank as soon as they started asking questions.

She went to introduce her husband to the producers, 

but her mind went blank when she tried to remember 

their names.

Sarah must have pretty bad stage fright because her mind goes blank as soon as she steps on stage.

Tradução: me deu um branco.