The form takes ages to load, then gets stuck at Page 1. It looks like it's looking for me to confirm that I have read the information and am happy to take part in the research, but there's nowhere to click to agree to this. Clicking on Next does nothing.
I am sorry to hear that people are having trouble filling in the questionnaire, I have just had a look on my laptop and my iPad and the form loads for me, so hopefully it was just a brief issue with Google last night. There is a question on the first page as pointed out by Fisherman, this is the only required question within the questionnaire so it does need to be clicked before you can access the second page.
I could not get past page 1 either, but I thought it was because I had to sign in to Google, I refuse to have a Google “account” 
You should not need a Google account to fill in the form. I believe this option is just to allow people to save their progress. For people who are signed into Google when filling in the questionnaire, no personal data (such as username) is obtained by the questionnaire, it is fully anonymous.
I have a suggestion for the layout of your survey ….
‘Back’ button is better on the bottom left …
‘Next’ button is better on the bottom right.
Currently it is too easy to hit the “clear” button on the bottom right where most surveys have the “next” button. (this is just a petty nit pick from someone who does thousands of online surveys) 
Thanks for the suggestion Ruskie. I don't know if I can change the button layout as this was pre-set by Google, but I will look into it.
And finally, a big thank you to everyone who has filled in the questionnaire so far! Your help is much appreciated.