This mac can't connect...

Every time I start up my Mac and go online I get a message that pops up saying this:

"This Mac can't connect to Facetime because of a problem with [my email address]. Open AppleID preferences to fix this problem."

Sometimes it says iMessage or ICloud instead of Facetime, but it's basically the same message. Thing is, I've never even used any of these things! I open my preferences to "fix" the problem but I don't see a problem, and I'm not even sure what the problem is or what I should "fix." I end up just clicking "Later" so I can look into it later. Then an hour later the box will pop up again and I'll have to just click "Later" again. Sigh.

Help!

Thanks.