How to fix my rode nt1a

Does the background sound get louder or fainter when you change the mic gain on your mixer? If it depends on your XLR cable, it may be radio interference, and you need to make sure you use top quality shielded cable, and that you're wired "balanced".

Repair of this mic is not something you can do yourself. This sort of failure is common, and I can repair it.

Removing the silicone bag and not using a pop shield can lead to condensation on the diaphragm. Place it in a bag of rice for a day to dry out any condensation on the capsule.
It may not be due to condensation though. Make sure your phantom power source is working. If possible attach another mic to the same source to see if it works. Check the contacts on the mic and also check the wire for any erosion or debris. If none of these work, fixing the mic may be beyond DIY repair.

The reason it is not being picked up by your PC is because the NT1A is a condenser microphone and it requires an audio interface that can supply phantom power (48V) to get it powered up. Without phantom power, the NT1A won't work. You many need to buy an external audio interface that provides phantom power to use the mic. Hope that helps.

The Rode NT1A requires phantom power of 24-48volts DC. The USB socket on your laptop will only supply 4.5volts.
The solution will be to buy a separate power supply or to connect it to your computer through a mixer that includes a phantom power supply option.

Assuming your preamp, cables, or room, aren't at fault, then your NT1-A is suffering from typical component failure and will need service. Even new mics of this type can be at the end of their useful lives, due to the cheap components used.

If it is under warranty, I recommend sending it to Rode for repair. Otherwise, I can service any Rode mic. Condenser Microphone Mod Service

It will need to be serviced. Condenser Microphone Mod Service

This is typical component failure, and the mic will require service. Condenser Microphone Mod Service