Why can't I access my eFile for 2018? I was able to input data a week ago. I'm not able to access now.

Well the Online program shut down 3 weeks ago so you could not have entered anything last week ... so are you now using the Downloaded version ?  If so you have to open the program on your computer ... you do not log in online. 

When?  A week ago?  2018 Online closed on Oct 15 almost a month ago.

How to finish a prior year online return   https://ttlc.intuit.com/community/prior-year-return/help/how-do-i-finish-a-prior-year-return-that-i-started-in-turbotax-online/00/26322

  And you will have to print and mail your returns.  So be sure to attach copies of your W2s and any 1099s that have withholding on them.  You have to mail federal and state in separate envelopes because they go to different places.  Get a tracking number from the post office when you mail them for proof of filing.