Can you click on something else in the side menu, like Deductions>Deduction Summary? If you use the Find tool (magnifying glass) in the top right, does it allow you to get to another page (ex: T4)?
You can also try clearing your cache or using another browser. This FAQ has instructions on how to clear your cache in many popular browsers: https://turbotax.community.intuit.ca/community/tax-topics/help/how-do-i-clear-my-cache-browsing-history/00/873530