I've been having my cello for a while now, but I've been busy with other instruments and I just started playing it again. I am a beginner, but it seems like my instrument is abnormally quiet and not producing a full tone. Any suggestions?

Well you might want to take a look at your strings, and see if there is anything abnormal with them. When strings get old or worn out, they can start to sound a bit muted and you can start to see wear on them; especially near the bridge and "the nut" or the top of the fingerboard. Of course it could also be an internal problem that you might want to get checked out. Also over time, if cellos are exposed to too much moisture, that can make it wear out more. I would bring it into your local music store (possibly one that specializes in stringed instruments, or at least sells them,) and tell someone there what the problem is, and they can determine if it's an internal, string, or bridge problem.

-Cole

Maybe you got used to the other instruments and in comparison, yours sounds weak.

It could also be from the strings, they could be getting old or they were never good in the 1st place. There are many different brands and each of them will change the sound of your cello.

What about the ROSIN on your bow? Is the bow sticking good to your strings?

Did the sound post fall out, LOL! That would be crazy/impossible, but that would cause a cello to get quieter.