Q: Cant close system preferences.

Hi, im in need of some help with my macbook air. An account was deleted around 6 weeks ago due to me and my partner splitting. I kept the laptop and he deleted his account. It still says on system preferences 'Deleting account' and I'm un able to close this. I was trying to download flash player but it said i have to close system preferences, which i can't! Can someone please help me close this window or tell me how to stop the account from deleting?

Thanks in advance, Katie.