With Microsoft Forms you can create surveys, quizzes, and polls, ask people to respond to them using virtually any web browser or mobile device, view real-time results as they come in, use built-in analytics to assess responses, and export findings to Excel for further analysis or grading.
A few reasons why your Form is not accessible anymore:
- You have manually closed your Typeform to new responses.
- Your account has reached its response limit.
- You have recently downgraded your account, and your form is using features that aren’t in your plan.
In some cases, users are unable to submit a response to a Form mostly because the deadline (submit end date) has passed.
- Login to Office.com
- Open the Form tab or go to Teams and open the Form from there
Open the form in teams > click on More icon 
> Settings button from the right top corner
Next proceed to Remove the start and end date.
Now click on the “Share” button to get the latest copy link and share with the respondent to get more responses.
If your Forms does not have a Start and End date, then you just need to reopen your Forms for more responses
Open the form in teams > click on the “More” button from the right top corner > Settings > click on the “Accept responses” at the “Options for Responses” list.