What Causes Erectile Dysfunction?

Hello , I am 29 old married guy. when I went to have sex with my wife. At bed room, first she removed her clothes, she became nude and later I have also removed my all clothes. After seeing her, my penis was not standing properly. It stood up for some moment and I pushed my penis (Have used condom) into her vagina but only my penis tip went inside to her vagina and it went down. After some time, I tried to bring it up by masturbate and till that time, the sperm came from my penis and again it doesn't standup down. So we didn't have sex. At last my sex was 100% flop.

I don't know what is proper cause for it

I am much worried about it..
what precaution's should I have to take for this problem???