You bet it can.
If you’re watching TV and all of a sudden you lose satellite signal, it’s probably not a broken LNB. Chances are, it’s a corroded cable, bad aim, a tree in the dish’s path, or something like that. But if you’ve eliminated all the other possibilities, it absolutely can be a bad LNB.
An LNB is a fairly complex and sensitive piece of equipment. It combines a super-low-noise amplifier, several antennas (at least three and sometimes more) and something called a “block downconverter” that takes the super-high-frequency satellite signal and converts it to frequencies that can travel over the average coax cable. That’s a lot of value for something that usually sells for under fifty bucks.
As someone who talks to a lot of DIRECTV and DISH installers, I can assure you that LNBs break all the time. The good news is that they usually break immediately, or they break after about 3-4 years. Despite the best quality control steps, some LNBs are no good when they get to the customer site. Something happens in transport, or there’s some unexpected static electricity that fries them when you’re hooking them up, or something like that. That’s why every installer I know has at least one of every type of LNB on the truck as an extra. As a regular person you can’t afford to do that, but you should know that LNBs do fail and it does happen. We do our best to help in cases like that but sometimes it’s just out of our control.