Flash suddenly stopped working !

Go to menu then shooting and turn on ttl

Assuming there's not really a fault on the camera. Have you got it dialed into a pre-set photo option ? This may negate the flash. Suggest going through the settings menu, putting everything to auto and trying again.

Try turning camera on,
Then press both Green buttons for a count of 10. This should restore factory reset.

Some models also have a reset button under a connector flap, or go into your menu. Under Custom Setting Menu, choose Menu Reset.

One of these methods should work.

You are correct in saying that the bulb needs to be replaced. Take the camera to any camera shop and they will replace it for you.

There is a switch on the hot shoe to detect the external flash. When you use an external flash, the switch will be pressed down, then the unit will bypass the internal flash and won’t let it fire. If the little switch gets stuck somehow, you won’t get your internal flash on.
Check this switch on the hot shoe (either on the left side or the right side), blow some compressed air then plug/unplug an external flash several times. Hopefully you can get it back

Check the playback menu that the review time has not been set to OFF. This will stop any pictures displaying on the back of the camera when taking them!

I leave mine at 2 secs which is long enough to quickly review and keeps the battery life up. If I need to review for longer, just use playback.

The flash won't come on if you have the camera in any of the creative modes (i.e. A-DEP, M, AV, TV or P). You can manually use it by pressing the flash button just above the lens release button on the front of the camera.

I had the same problem, "BBWS" found this "solution":
Turn the camera on as if to take photos (not to review photos).

Press "Home" (upper left corner)
Press the camera tab (bottom left-most tab)
Press "Scene Selection (SCN)"
Press "OK" at the "Select type of scene" prompt

However, I still don't have flash available in the PGM or AUTO modes, which tells me it is still broken.

try resetting the camera back to factory defaults by putting camera in P mode, menu, custom reset

Top of the camera, lightning bolt like button. When you press it while the camera is on, it will bring up a menu, there should be an option in there to shut it off.

I had the same problem with my flash not working on any setting, but I found a way to fix it: hit the menu button, make sure the "rec mode" choice is set to normal instead of burst. I think the burst mode takes multiple shots in a row, so the flash isn't compatible with that setting?