Go through this
Troubleshooter

I'm going to agree with Sami and then get ready for the worst thing ever - especially if you don't have a good recent backup.    It's possible the form is corrupted or a subform is corrupted.  It also (my 2 cents) be needing a Compact and Repair.  I had a backup but it too was showing signs of becoming corrupted :(.

I have a project that I'm rebuilding from scratch because all my VBA in the Project Editor(Not including my modules) and some forms just vanished.   I knew what I had done wrong so the loss was as bad.

Good news for me was my tables were fine.  No I hadn't split the database and didn't a need to (at the time).

I'd backup/copy the form.  Then start pulling parts of it out until you find the culprit.  A baaaad subform has made my parent form not want to play nice.

On my current project that went live last month, I have over 650 saved versions. Diskspace is cheap. Apart from the departmental automatic saves, I save my work when I am developing several times a day to the next version number. Full copy every time. At least 3 times my DB gets corrupted, and I needed to go to back up. Never lost more than an hour or two worth of work.

I make 2 copies - one on my local drive and one on the network drive.

Drive space is cheap until you have SSD drives and then (actually not bad), but compared to SATA drives.  My older computer has 6TB (multiple SATA drives), it lacks the speed of this one.  Between the SSD drive and the other I have 1.5 TB (Haven't gotten close to killing yet), and an external drive.  My old problem was (I didn't back up often enough when I started this project).  Since I'm the only one using it.  I have button that automatically backs it up before access closes.  Can't stress enough - especially while developing to do a lot of compact repair.

Jeffrey, is there a video somewhere of how to make that button that auto backs up your database?

Backup Access