So i create a level, save it EXACTLY as it says on the tutorials. I open JK and start it, and when i click "new level" and then start, it just flashes and goes back to the level select menu. Someone please help me, this is driving me insane. Thanks.

We need more info.

What level is it? Any mods being run?

What exactly do you mean by "flashes and goes back to the level select menu"?

umm, it's my level. and what i mean by "flashes and goes back to the menu", i mean "flashes and goes back to the menu". it just flashes, and goes back to the level select screen.

and no mods are being run.

'Flashes' isn't a good description, does it 'flash' meaning you can see the level for a moment? 'Flash' white and return to the level select screen? 'Flash' multiple times? You need to be more descriptive if you want help.

JED or JKedit?
If JED, make sure the consistency checker is clean.

Otherwise:
Any cogs in the level?
Does one of the cogs tell JK to endlevel()?

It flashes once very briefly and goes back to the screen where you select the levels. It does NOT go into the level. What's a consistency checker? hehe :$. No cogs in the level at all.

Make sure you have walkplayers.

And make sure said walkplayer is in a sector.

Consistency checker - F10 - will check the level for errors. I bet your walkplayer isn't in a sector....