Lost the ability to fold code in eclipse

I have lost the ability to fold my code in Eclipse (Helios).

I have always used ctrl + Shift + / but now it's not doing anything in one particular project and also all the "+" signs have vanished from the left bar.

Can anyone tell me what I have done? In another project it's fine, but the one I'm currently working on I can't and it's so frustrating!

How do I collapse all codes in Eclipse?

If you are using PyDev in Eclipse, its Ctrl 0 and Ctrl 9 for collapse all and uncollapse all respectively. Ctrl - and Ctrl = to collapse individual methods when your cursor is on the line of the method declaration.

How do I enable code navigation in Eclipse?

Ctrl + F7 : Dropdown with the available views. It allows you to switch from code editor to the Navigator view (so you can open other files)

Folding is configured under Window -> Preferences -> Java -> Editor ->Folding

The Preferences window has a search box - very useful to find even the most obscure options.