Yeah, it sounds like it's the 4 in 1. Did the rotor get blocked while power was being applied to the motor? If so, it probably burned out the MosFET for the main motor channel.

If you've only had it a week, Horizon Hobby might replace it for free. You should contact them.

Also, I know some people have been able to get replacement FETs and fix it themselves. If you have good soldering skills, you should search the forums to find the info about this.

I don't know of the 'best place' to buy a new 4 in 1, but it shouldn't cost you more than about $70.00. Just google it, and compare prices.