Yeah, your first one kinda looks like you went into Photoshop and just composited the black wall behind it or you just selected the wall behind and edited that one and left the bike and floor alone... either way it looks off. Also the bike itself looks out of focus too... maybe try working with different compositions, try taking it at different angles.. or maybe even just get closer. NikonME makes a good point about the flower too, at first I thought it was some type of logo and I really didn't get it, which I guess if you want, you can use it as one. Haha.
However, I think what happens, and I am guilty of this too, is sometimes people edit too much which is what happened in the first photo. Generally speaking, at least from what I have gotten out of photography at this point, is if you are trying to get some type of effect or "coolness" to your photos, is try to do them pre-production, maybe take the photo in Black and White and try to up the contrast later, or maybe there is some sort of filter, I don't know, whatever it may be. Then later, if you photo is too bright, colors seem a little saturated, or if you are doing photo manipulation, which could a possible thing you might be doing with the dark theme, then you go into Photoshop or Light Room, or ever program you use for photo editing, and make those changes.
Do you happen to have the orginals of these photos? I'd love to see them and see if there is some things I can try to suggest.