Is you mortgage connected to the lender? If so, you will not have an account register so no payment details will be able to be entered. With connected loans the lender downloads current balance and not much more. It's kind of like Simple Investment Accounts which show high level summary of account value but no transaction details. It's great for people who don't want to track all the details and just want to see the current balance but not great for those who want to track the details.
To enter payment details the loan must not be connected to the lender. Only unconnected loans will have account registers. To change a connected loan/mortgage to a manual loan/mortgage you can go to the Online Services tab of Account Details and click on Deactivate. Or you can delete the mortgage account and start over but don't set up a connection with the lender.
Do you have a recent backup file from just before whatever happened to "screw up your account" that you can restore to see if the register is still there or not? If so, what kind of account is it set up as in that restored backup file (it should be shown on the General tab of Account Details)?
What was the event that triggered all of this to occur and when did that happen?
I've read that some loans set up from a long time ago (pre-2013) were set up in Quicken not as Loan accounts but as connected credit or liability accounts which had registers but that the account type was somehow changed to Loan and then the register was no longer visible. This can sometimes happen during account deactivation/reactivation and when the financial institution connection is completed the account type gets changed to what the financial institution downloaded.
There are some prior posts that talk about this issue in more detail that you might want to read with some posts sounding a bit like what you have described. They won't tell you how to fix the the situation but they do provide some additional background information.:
