Prior to continuing, I'd like to make sure the issue you are encountering is not occurring as a result of an application conflict. The best way to proceed would be to try loading under a new Window's Administrator account and in a "clean boot" state.
Create a new Windows Administrator (<--important that its an Administrator) account:
Log in under that account and try. If it fails, and while still under that account, please click the link below for performing a 'clean boot' under it:
After you've loaded Windows in a clean state, please try once again.
Once you are booted into a clean state, you may need to Install the Steam service again. You can do so by trying to start up Steam. If Steam asks you to install the Steam service, simply hit "Install Service" and try to boot up Steam again:
Let me know.