It sounds like you may be experiencing a common issue with the Auto Fill function in Excel 2007. Here are a few things you can try to fix the problem:

1. Check your Auto Fill options: Click on the Microsoft Office button, then Excel Options, and then Advanced. Scroll down to the Editing Options section and make sure that "Enable fill handle and cell drag-and-drop" is checked. Also, make sure that "Extend data range formats and formulas" is checked.
   
2. Try using the Auto Fill Options button: After you have typed in your initial values, click on the cell that contains the first value. Then, click and drag the fill handle (the small square in the bottom right corner of the cell) down or across to fill in the rest of the series. When you release the mouse button, a small Auto Fill Options button will appear. Click on this button and select "Fill Series" from the drop-down menu.
   
3. Use the Fill command: Click on the cell that contains the first value. Then, click on the Home tab, and in the Editing group, click on the Fill button. From the drop-down menu, select "Series". In the Series dialog box, select the type of series you want to create (e.g. linear, growth, date, etc.) and enter the appropriate values. Click OK to fill in the series.
   
4. Check for updates: Make sure that you have the latest updates for Excel 2007 installed. Click on the Microsoft Office button, then Excel Options, and then Resources. Click on "Check for Updates" and follow the prompts to download and install any available updates.

Hopefully one of these solutions will help you get the Auto Fill function working properly again. Good luck!