Having Trouble Running An SQL Update Statement

Forgive me but I'm relatively new to SQL.

I am trying to update a column of a table I created with a function I created but when I run the Update Statement, nothing happens, I just see the underscore flashing (I'm assuming its trying to run it). The Update Statement is updating around 60,000 fields so I assume it should take a little while but it's been 10 minutes and no good.

I would just like to know if anyone knows just some general reasons that the underscore may be flashing. I know this is super general but I've just never seen this before.

Here's an image of what I'm talking about: http://ift.tt/1P6hA1q