The options are, you need a new antenna, or make sure everything is grounded properly, check for a "blue coil" near where your antenna is and make sure its there if you don't see one you won't get service or it might be loose giving bad service. Another option is to hard reset it again. Also make sure the connector has a secure connection to the board, it might also be loose.
It's as simple as that blue coil thats right beside the antenna connector. If that blue coil is gone you will get no signal. Soldering the joints together won't fix the problem, you will need to find a new mobo or solder a new blue coil on it. Thats the only way to fix this problem.
Very simple, look up your iPod on youtube for the teardown of it. Make sure you have all the screwdrivers and proper tools. Also make sure you don't rip anything inside. For the normal iPod I believe its just a flex cable you need to replace, but if its a iPod touch its a solder job. Either way take it slow and its a pretty simple repair.
practice makes perfect, use to take me an hour to do the full repair of touchscreen replacement or anything. I learned that other technicians in the area do it in 20 minutes. This was starting to become a turning point for customers. Each repair now takes me a total 18minutes for the iPhone full repair. I use to follow the tape ways, etc but that was really slowing down the process. My solution to you, when you take a screw out place it in front of you where u took it out, and make an invisible phone. So when u put them back you just put them back where they came from based on the invisible phone. Its also mostly you have to memorize each screw, its not as hard as you think. iPhone is one of the quickest and easiest repairs out there.
As the other guy responded, buy some isopropyl alcohol and put a bit of it in a toothbrush. Scrub your mainboard wherever you see corrosion or any parts under suspect. This is a common water damage repair, the problems lies onto your mainboard that has corrosion on it.
When you do the repair on the screen there is a hole where the light sensor is, cover it with a black marker. Can also cover the sensor with a black marker, this problem usually occurs during a new white digi replacement. All your parts are probably fine, its just needs the black marker and this generally fixes the problem 80% of the time.
yes you can replace just the glass which is LCD screen or also known as digitizer. you can buy the LCD screen on websites easily by looking up the model and could look up the teardown for it if you are willing to do the repair yourself.