In short, if someone does not respond to a Congressional subpoena, they can be subject to proceedings for inherent contempt, criminal (statutory) contempt, or civil contempt. In inherent contempt, the Sergeant-at-Arms does bring the person to Congress, where they are tried and are subject to imprisonment to the end of that term of Congress. In criminal contempt, a statute requires a U.S. Attorney to bring the contempt charge before a grand jury; the law provides for a fine up to $100,000 and up to a year in prison. Civil contempt involves suing the person in court.
All of that is true. However, it does not speak to the issue at hand. Congress has no independent law enforcement authority with the power to arrest, indict, etc. All federal law enforcement authority exists as a function of the executive branch. In other words, Congress is utterly impotent against an executive branch determined to resist it.