Help with nesting IF statements

[mesteptoe]

I am working on a project calendar, i.e Weeks v. tasks

As a task is started I want to get the cell relevant to that task and that week to show "Y" and turn RED. I am using the following statement in each cell to do that,
=IF(AND(G8>=$E$21,G8<=$F$21),"Y","") where G8 is the current date, E21 is the date the task starts and F21 the finish date for the task. Now this works fine as long as a finish date for the task (F21) has been entered. Once the date (G8) exceeds the task completion date (F21), the cell is left blank as it should be.
But if the task has started, i.e. E21>0, but not completed, i.e. F21=0 the schedule is left completely blank - as expected. But I need to show RED coloured cells to show the task is in progress.
Somehow I need to link another formula to the
=IF(AND(G8>=$E$21,G8<=$F$21),"Y","")
i.e. =IF(AND(G8>=$E$21,$F$21=0),"Y","") such that two sets of criteria are checked out. Is it possible to link the two statements together with an OR statement? If so, how do I do that?

Thanks for your help.

Regards

Graham

 

[mesteptoe]

Well that's correct because it's impossible to be undertaking a task at a date beyond the current date