blank means "empty " so "come up blank "means I can't think of an answer" "I can't think of what to say" "my mind is empty"

Thank you.

To "come up blank" is generally seen in computing terms, when you click on a web link and you just get a blank page i.e a page with not text or pictures appearing. There is also a phrase "to draw a blank" which means that you are not able to find or remember a certain thing. For example, I searched the internet for the meaning of "come up blank", but I drew a blank.