1) IF you are using ONLINE Turbotax, you have to be logged into the exact-same UserID you used for last year's tax return.
2) if you are using Desktop software, you must have the 2017 tax datafile ( .tax2017 file extension ) on that computer system's hard disk....and then you must select that 2017 datafile as the transfer-in file right at the very start of a NEW tax return.....cannot be done alter.
3) W-2 ...those are never imported automatically.......you initiate the import yourself in the W-2 section. IF you can't get the import to work, you just use your paper copy and enter the information manually form your paper copy.
____________*Answers are correct to the best of my knowledge when posted, but should not be considered to be legal or official tax advice.*