If Blank Cells, Paint Yellow. If Cell To Left Is Less Than A Number, Don't Paint

I have a spreadsheet which contains 39 columns with a header row. The number of rows varies per spreadsheet. I'm running into a problem with highlighting(painting yellow) cells. Really the problem is selecting the cells to be highlighted. The macro is skipping some of my code completely and in other cases leaving some cells unhighlighted.

1. All blank cells in row AG should be painted yellow.

2. If column AF contains a cell with number 900 or greater, then the cell in AG (same row) should NOT be painted yellow.

3. All blank cells in rows AC and G should be painted yellow. Some spreadsheets may not contain blank cells.

Problem with the VB is not performing the code after the first command. It will highlight MOST of the cells in AG but for some reason it is leaving a few blank ones unhighlighted. The blank ones are usually at the bottom of the rows. I have no idea why it would miss these.

I believe the "ucase" tag is incorrect since its looking for a number but I am not sure what to put in its place and if I use something else should I dim it as ""?

I've attached an excel spreadsheet which contains a sample to this problem. I've also attached what it should look like if my code worked.