As a mark of >100 is an error, and it doesn't matter whether all the other marks have been entered and it does not matter whether the marks indicate a pass or fail, so you need the new condition to be tested first.
Move the existing two formulas down and add this one first:
As you already have green for pass and red for fail, I suggest using a different color for this - I used yellow.
As before this new formula can be used for the text - it is also added at the beginning so that it is the first test performed:
I have split the formula onto three lines, for ease of viewing - join it back together before pasting it into a cell.
You could add a modification of the first conditional format formula on its own to all the cells containing the individual marks, so that any cell with a mark greater than 100 is highlighted. Add the formula to the conditional format for the first cell in the range, testing only that cell. If the first cell with a mark is B2, then the test is for B2>100. (Use B2, not $B$2 as you want the formula to change for each cell in the range). Now Copy the cell and 'Paste Special' - 'Formats' to all the other cells that contain or will contain marks. All these cells will now respond to a mark of >100.
In your response you said am trying to do it, but its not working. It would be helpful if you said what you had tried and what was not working and also included any formulas you had used. This would help the learning process as it may be possible to identify what was wrong and why you were not getting the expected results.