Possibly!

Can you unlock those input cells and protect the sheet. This will cause the
upper leftmost cell to be active (selected) when the workbook opens,
...usually. It depends where it was when last save, but you could add code to
Workbook_BeforeClose() to activate the starting cell so it's "ready-to-go"
when it opens.

Using just the Tab key will only allow navigation horizontally
left-to-right, and will proceed down to following rows when the there's no
more unlocked cell in a row.

If you don't need users to have access to non-input cells, they can only
follow the Tab key's route. It would be a good idea to review the design of
your sheet so this follows a logical order. In some cases, users may want to
use the other navigation keys in concert with the Tab key. Note that all
other navigation keys will also work 'normal' on protected sheets, but their
behavior can be dis-orienting if you're not used to using them with protected
sheets.

Regards,
GS