Why is my iphone camera doing this?

I have an iphone 4 running an early ios4 that is jailbroken but I don't see how jailbreaking has anything to do with this because its been working for like a year until now.

I was filming on a beach shore in the water (I did not drop it anywhere so it can't be water or sand)
and I minimized the camera when I was done when suddenly a big military cargo plane was flying low overhead and I wanted to record it and I very quickly opened the camera and the shutter would not open at all! I tried turning it off and on, holding home and power buttons til it turned off (hard reset?), clearing the cache but it will not open. The little switch that you slide to switch from camera to camcorder just flickers very fast and the shutter doesn't open.

How do I fix this?

Turn it off by pressing the lock/power button. Then leave it alone for like a few seconds or minutes, turn it back on. Go to the camera and try doing it again. If it didn't work, I suggest you should go to the Apple Store or whatever store you got your iPhone 4 and they will see what's the problem & fix it!