When I have a pdf open and try to to sign in on my computer, as soon as I click "sign in" the window pops up but then disappears. This only happens on one of my computers. This has not happened before.

Hey Louis,

Please conform whether you are signing up at https://cloud.acrobat.com/ or using Adobe Reader for the same.

If you going online, then please check that you using your correct Adobe ID credentials. You might also check with your internet connection and try using a different browser.

If you are using Reader, then let me know what version of Adobe Reader are you using.

Try signing up with a different PDF open and check if the same issue persists.

Hope to get your response.

Regards,

Anubha