Since you said "internal keyboard" I'm assuming this is a laptop? If so, what brand and model?
The most common problem is that something small gets underneath the key and jams it. You can tell this is happening if the key does not depress all the way. You can try to clear it by pounding on the key really hard or holding the laptop at different angles and try to blow under the key real hard (compressed air is good for this). If that doesn't work, you can usually remove the keyboard from the laptop (usually by screws underneath, although sometimes you have to disassemble the top bezel to some degree first) and try the same steps again.
If the key has full travel and the keystrokes simply aren't registering, it may just be time for a new keyboard. Armed with your laptop's brand and model, you should be able to find a replacement on Amazon or eBay pretty easily. Most of the ones I've ever bought are usually in the $30-50 range.