Grey screen - UXtheme patcher

I have tried to apply a theme of not my windows version, then it gives me please wait screen to apply it then a Grey and black screen even whenever I reboot or go to safe mode
My access to the windows for now is a command promote startup
So how can I change the default theme again to get my windows visually works, or any ideas about solving the problem please?
Thanks in advance

type rstrui at the command prompt to run the system restore. see if that works.

Thank you a lot, but it didn't work, and I have tried to boot a repair disk that let me see my windows drive from it I have deleted the wrong theme, thank you