Up until last week I could insert tabs into my code to my heart's content. I could align my code just the way I wanted so it was easy to read. But now I can't, and I cannot work out why.

Smart indent works a treat, and always has done, but now when I hit TAB either:
(a) nothing happens at all; or
(b) the current line smart-indents itself if it hasn't already done so.

This started happening right after I went into the Tools->Options menu to change the opacity of commented code, yet I can't find what else I inadvertantly changed. I've messed about with the options for 'smart', 'block' and 'none' yet the TAB key is still ignored.

Sometimes I have to open notepad and write random words with tabs inbetween to calm myself down. Help.