I recently bought an alpha trek bike for 50 dollars and the bike needs repair. I have not ridden a bike for almost two decades and had very little information but since I needed one in a little budget I bought this one. But the chain seems to be coming off the moment I start peddling. Front derailleur is broken and the crank is loose. Does the whole chain needs to be replaced? Or the front derailleur and the tightening of the crank will be enough to fix it. I will really appreciate your feedback. I tried uploading pics but I can't do that unless I have posted 10 times on this forum.