Thanks for reaching out to us in the Community, @sandy8.
I'm here to help make sure that you can print checks in QuickBooks Online (QBO).
Just to confirm, did you get any error messages when printing them? If so, may I know what's the error? Any additional details will be much appreciated.
In the meantime, let's perform some troubleshooting steps that can help us isolate this. Try logging into your QBO account using a different or a private browser. There are times that the browser is full of frequently accessed page resources, thus causing some errors and/or unusual responses.
To use a private browser, here's how:
On your keyboard, press Ctrl + Shift + N (Google Chrome).
Ctrl + Shift + P (Firefox or Internet Explorer).
Control + Option + P (Safari).
Once logged in, try to reprint your checks again. For your reference, you can also check out this article for further guidance: How to print checks.