My nikon d40 flash won't pop up. How do I fix this?

It just won't pop up, i think it has a small lock but i don't know why its not working, it worked well just a few minutes ago… The battery is full by the way, so its not that.

Ps. I would give as much points as you like, this is very important, just tell me how to fix it.

You really must google "fix repair nikon d40 flash" or similar

you'll find quite a lot on this

Chances are you are simply in the wrong mode.
Get out your user guide - you should know that book inside out, anyway.

If you lost it, download a new one.