As usual, I follow up Alec, who makes a good suggestion, and add a little more detail. Your receiver is a Marantz 2220B, a '70's product. It has 20 watts per channel, and if in good shape, will sound pretty good, with a solid low end, and a sweet, slightly rolled off top end. But, it needs efficient speakers to produce large scale sound. You can get it to play loud, but you will need to be pretty close to speakers. I have one, and that's how mine behaves.
Anyway, the service manual for Marantz 2220B is found here. http://www.hifiengine.com/manuals/marantz/2220b.shtml
This is the VE companion website HIFI Engine, and you will have to start an account to download the manual, which is for free if you have an account. Just go to top of page, at right, next to the search block, and click on HFE.
The manual has a good diagnostic procedure to help you figure out why your FM doesn't work. Be sure that you out an FM antenna on the unit. Even a folded dipole, or 5 or 6 feet of stranded insulated #20 wire will work. Stick 3 feet in each 300 ohm antenna hole and adjust wires for maximum signal pickup. When you play AM be sure that the AM bar antenna on back of receiver is fully down and away from the back. This will increase the number of stations you get. You may have to rotate receiver to orient it toward your favorite AM station.
The hum and weakness in amp could be a power supply problem such as a bad rectifier or bad filter capacitor. My experience is that dirty controls such as Alec suggests usually behave erratically, and unit will behave properly when controls are wiggled. You can also just cycle the controls, even without cleaner, and this sometimes will cure the problem. Won't hurt to shoot controls with Deoxit or other contact cleaner, but may not cure your problem. Manual also shows specified voltages on chassis and the schematic diagram, which will guide you to likely failure points.
Any unit this old can have more than one problem at a time, and you will have to cure them all to get it to work properly. You will just have to figure it out a little at a time. You can use another amp with a .1 mFd 400 volt capacitor hooked to input as a signal probe to trace the sound through the amp. Tie test amp chassis to the chassis of amp under test to pervent hum. At some point, the sound coming through the test amp will identify the bad stage. BE CAREFUL! If you have not serviced a unit such as this, you may have to get some help from an experienced person so you don't inadvertently get shocked. If you can't read the schematic diagram or the block diagram, you will need some help to decipher them.
Take a look at manual and see if it assists you in feeling confident. If not, you may have to hire the job done, or get assistance from an experienced person. Job is doable, but may not be easy, and there is some risk. There are Youtube videos showing people servicing amps like this, which may show procedures and safety precautions.
And good luck from the old manual reader, and Youtube watcher,