We haven't received similar reports about QBO being down or unresponsive, reginamater.
The cache stores temporary internet files from your browsing history to help your browser quickly load the pages. However, too many files may affect the browsing performance and may require you to clear it out.
Let's try to do a few browser troubleshooting steps to get your account working again. Start with opening QBO in a private window. If you can open the Checks, Bills, or Pay Bills tab, go back to your previous browser and clear the cache. You can also use different browsers to check if it works there.
I'd be glad to know if you're able to access these tabs after following the steps I gave. Just leave a reply if you need anything else.