I just replaced the batteries in my HP 12C calculator and when I turned it back on the display looks like this 0,000. How do I get the display to show decimals instead of a comma?

Hello,
Here is what the manual for the HP 12C Platimum financial calculator says on page 17 of 275

Digit Separators
As a number is keyed in, each group of three digits to the left of the decimal point is automatically separated in the display. When the calculator is first turned on after coming from the factory — or after Continuous Memory is reset — the decimal point in displayed numbers is a dot, and the separator between each group of three digits is a comma. If you wish, you can set the calculator to display a comma for the decimal point and a dot for the three-digit separator. To do so,
turn the calculator off, then press and hold down the [ . ] key while you press [ON] Doing so again sets the calculator to use the original digit separators in the display.

Hope it helps.