Accents option when hold down keys disappeared

Hello,

I am mid writing my dissertation and studying languages; I have always been able to hold down a letter bringing up a selection of accents to use (a bit like it does on an iPhone keyboard).

For absolutely no reason, today that feature has disappeared. I havent updated my laptop or changed any settings or even turned it off.

The accent use is vital for my exams coming up next week.

I have read the forum, changed the 'Key Repeat' to 'off' and still nothing. I'm mildly freaking out, please please can someone help me.

Many thanks in advance.