There are times that the browser you're using is full of frequently accessed page. This will cause some unusual responses like a blank screen. To isolate this, you can log into your QuickBooks Online (QBO) account using a private browser (incognito).
Please note that before you cancel your account, I'd recommend exporting and printing your data for future use.
To start, you can refer to the following keyboard shortcuts below to access the incognito window:
Press Ctrl + Shift + N (Google Chrome).
Ctrl + Shift + P (Firefox or Internet Explorer).
Control + Option + P (Safari).
Once done, go to the Gear icon, then select the Account and Settings menu to cancel your subscription. If it works, return to your default browser and clear its cache and cookies to refresh the system.
Moreover, if the issue persist, I'd recommend using other supported browsers to perform your task.