MDB opens small.

[Steve_in_Kent]

I have an .MDB using office 2010. A strange behaviour has just started happening.

Instead of the database opening full screen. the database window appears as a small box in the top left hand corner, you can maximise it by clicking on the square box. but it never used to do this.

the on open even has code like DOCMD.MAXIMISE

etc.

[HansV]

Access doesn't store a specific window size / window state for each database, just the window size and state of the Access application. There must be something - VBA code or a macro - that causes the database to be displayed in a small window. Check carefully whether some code or macro interferes with the DoCmd.Maximize command.
Without seeing the database it's difficult to guess what else could cause this.