How can I use my Mac again?

Hello!

I've recently TRIED to delete all my files using the Cmnd+R thing at startup. Everything was going great until I remembered that I wasn't able to add some files to my external hard drive. So I switched off my laptop while it was on the pass 2 part of deleting because I set it up to most secure, the one with 7 stages. When I switched it back on, it loaded with the apple icon for a while then suddenly it was replaced with a no symbol. I've tried holding down shift and pressing command+r but it still returns to that. Please, please, please help me! I know I'm an idiot for doing that but please help me. 😟