Excel no longer autofilling cells containing data validation lists

Hi,

I input hundreds of lines of data each day and up until yesterday evening was able to simply type the first letter of a required value to automatically prepoplate a cell containing a data validation list. The lists only contain 2 to 4 values. As from this morning, excel has started asking me to select the required value from a drop down box which appears when I start typing, or to write out the whole value manually. This is incredibly time consuming given the number of cells I complete each day. I have scoured the internet for a solution to no avail. The standard "turn on auto-complete" seems straightforward but this setting has always been switched on. I have found some solutions suggesting a large piece of code or a combo box but given this problem only started yesterday (with no updates inbetween) I feel there must be a simpler solution.

Any help would be much appreciated!