craftgrrl | You are my last hope (Reply)

The subject accurately describes my desperation.
I am a new middle school teacher in Los Angeles and I arrived in my new classroom this past week to find my projector screen completely tagged up. A well-meaning veteran teacher comes in a sprays white schellac on the screen and... it makes it look worse. He then comes in with a miracle solution (clorox-soapy concoction) which effectively removes the rest of the tagged mess. My problem is I still have some shellac that is on the screen and only seemed to enhance the graffitti (there are some profanities in that area... great).
So... I was wondering, since many of you have the ins-and-outs about paint, is there anyway that i can remove this paint? I'd like to be able to use this projector screen.
Thank you, you wonderful people you.
Hm... and my most recent, crafty adventure? Making bulletin boards for my classroom. I'm sure none of y'all actually want to see that. :)