Ok, so lately I've found my E string keeps popping out of the thing that the strings through between the headstock and neck. I know this thing has a name, but it's completely slipping my mind now. Looking at it, I can see that all the other strings are sitting in these things, but the E is just barely sitting in it. I tried pushing it in but it did nothing. I do hit the strings quite hard, but I never had this problem before. I tried playing much softer, and it's still coming out.

Any idea on how to fix this?
The part is called the nut. Sounds like you need to file a deeper hole for your string to sit in. I wouldnt recommend doing this if you dont know what youre doing you will make it worse. Have it done at a shop.
Better than your G string popping out
I love my keyboardist, he's hot.

Quote by phlip999
The Pit is the epitome of higher learning and full of intillectual people who help the masses solve their problems.

The Llama Forum Bagel Group
i agree with damage, but it's really not that scary to do it yourself. it just requires some careful, gentle filing with a fine rasp. if you can't do that, then you should see a luthier about it.
"Hey kid. You wanna cigarette?"

"No thanks! I/m already hooked on Fonicks!"

have you changed string guage recently? I would think twice about filing the slot deeper since this will lower the action and possibly result in fret buzz.
Is there a gap between the string and the bottom of the groove? Because as Rusty_Chisel is guessing, it sounds like you've changed to a thicker string gauge, and then it wont fall into the groove without widening it (don't make it deeper, just wider).
Actually, when it first happen I was using the strings I would normally use, but I couldn't get it back into the slot so I changed them. The strings I changed to are a brand I haven't used before, but they're the same gauge (0.10) but I can easily pull it back into place now without it even going out of tune.

There does seem to be some space between the string and the bottom of the groove. I'll probably just take it to the shop, I'm not very comofortable filing it myself.