Severe mask lag!

PS had been working perfectly fine for me until a few days ago.  When I have already selected my subject and then click the SELECT & MASK button, that is where the trouble begins.  There is a 5-second lag when I try to make any changes with my brush in the masking window.  

To try to answer the things that you are wondering...

I made absolutely no changes to my PC.  The computer is only 6 months old and is a very good one.  After being really frustrated with this issue, I updated the version of PS.  Nothing changed.  I have restarted the computer.  I have used the PURGE function.  Still nothing.  The masking window is the only place where I have any lag.  Otherwise, PS works flawlessly.  

Any ideas?  I could really use the help right now, as I am need to mask 6 baseball & softball teams out of green screen shots.  Thank you!