The 2018 program must be downloaded, installed and updated before it will run. Not sure where you bought the program ... but if you did from TT direct then you should have an email with instructions and the correct link ...
Use this download link to retrieve your purchase:
Or this one : https://shopping.turbotax.intuit.com/app/downloads
If the download file isn't there, then look to see if you have multiple accounts (User IDs), and if the download might be in another account. To get a list of your User IDs and recover account access, you can use the tool at the link below. Try using your phone number first. Once you know all of your User IDs, then try each one at the download link I provided above.
NOTE: Before running the account recovery tool below, log out of all Intuit accounts including this user forum, or you might end up in a loop. Then clear your browser Internet cache, close your browser, then reopen it, and go to the link below. You may wish to copy this link so you can paste it into the new browser session.
If still no luck after running that on your phone number and each email address you have, then run the tool yet again, but this time choose the small blue link that says "Try something else", and it will look you up by SSN and other parameters.
Remember that you do not "log in" online to use 2018 desktop software when you are ready to prepare the 2018 return. You put the software on your own hard drive and use it by opening up the program on your computer. Your 2018 return will have to be printed, signed and mailed, since you missed the deadline to e-file.
When you mail a tax return, you need to attach any documents showing tax withheld, such as your W-2’s or any 1099’s. Use a mailing service that will track it, such as UPS or certified mail so you will know the IRS and/or your state received the return.
If you are getting a refund, there is no penalty for filing late. If you owe tax due, then file and pay the amount due as shown on the Form 1040, but expect a bill later from the IRS for the penalty and interest you will owe. Only the IRS will calculate this—TurboTax will not calculate it.