Is the AC power on? That is, is there any indication (power light, etc) that the power is on? If not, and assuming the house circuit breaker didn't pop, you may have a blown fuse or thermal cutout. These are usually located on the control board, behind the control panel.

When electronics get a dose of fresh water, they can sometimes be saved. But saltwater is nearly always fatal. Even if the device does not fail immediately, soon the salt will short something on the PCB. Don't even try to get it fixed, just replace it.

The Macbook communicates with the charger via a communication protocol known as "1 Wire" which is used in some Maxim semiconductor products. If you look at the MagSafe or MagSafe2 connector, you'll see it has 5 pins. The two outermost pins are GROUND, the next set of two pins are + POWER, and the center pin is SENSE. The SENSE pin is allows communication between the MacBook and the Charger. The charger implements this communication with a Maxim DS2413 chip in the charger which returns a 64 bit identifier to the MacBook. This ID is used to identify the charger model, wattage, serial number, and charging status. The MacBook can both read this ID and write to the DS2413 to control the multicolor LED in the MagSafe plug. There is a good writeup of the process in Ken Schirriff's blog at: http://www.righto.com/2013/06/teardown-and-exploration-of-magsafe.html as to how this works. I suspect that the reverse polarity damaged the circuitry that controls the charger-to-MacBook communications on the MacBook side. My...

I assume you've tried another set of headphones to ensure that that is not the problem. You might also check the obvious culprits such as that the volume is turned up for the particular source you are using in the phone's mixer, and that Bluetooth has been temporarily turned off to ensure that the phone doesn't think it's supposed to be talking over Bluetooth rather than over the headphone jack. Other than that it's likely the jack has failed and if so there's no choice other than getting the phone repaired

You said that you trimmed the flat cable. Even though it may look the same, the part that you cut off has a short section at the end that is usually conductive, whereas the rest of the cable is insulated. So once you cut off a bit the end of the cable is now insulated and will not make contact with the connector. Depending on the design of the cable you may be able to recover from this. What you need to do is remove that insulating layer from the last 4mm or so of the cable. If you look at the connector, you will see metal contacts one side, usually the printed circuit board side. That, is the side of the cable that you're going to want to make conductive by removing the insulation which is usually a layer of very very thin plastic or lacquer. Try this: get some 1000 or 1500 grit wet-or-dry sandpaper from an auto parts store. GENTLY remove the clear insulating layer at the very end of the cable without also removing the conductive traces. Depending on the type of cable this may or may not be possible to...

You didn't mention it, but I am going to assume you have a laptop. If not, try replacing the desktop's wet keyboard - they are cheap and you probably can't fix the old one. On your laptop, if it is a small amount of clean water sometimes all you need to do is get everything dry. Trapped water can stay liquid for a long time, so it is best to apply a small amount of heat. If it is warm outside, put the laptop in the sun for a few hours with the LCD open. Or, use a hair dryer - NOT a heat gun - directed toward the keyboard from a safe distance, about 12"-16" (300mm-400mm) for an hour or so. Don't overheat the keyboard; if it is too hot for your hand it is too hot for your keyboard. Of course, never let a hair dryer run unattended. If this does not solve the problem, and the symptoms are limited only to the keyboard, you need to replace your keyboard. This is usually a simple repair. Check for a guide on this website to show you how to do the replacement, and then Google "laptop keyboard" to find a...

What you have is probably a counterfeit, or fake, battery. A real Motorola battery has a chip inside that controls charge/discharge and allows the phone to identify it as being a real OEM (original equipment manufacturer) battery. Most batteries sourced in China and sold on eBay are not OEM batteries, they are fakes. They may look the same on the outside, but they are not the same on the inside. If the phone can't validate the battery it will either display a warning, or not charge at all, depending on the phone. There is a good reason for this. To save cost, counterfeit builders often buy rejected lots of cells, and/or leave out safety components. A few years back there was a rash of phone and digital camera fires traced to defective batteries, and they turned out to be fakes. This led to the new generation of "smart" batteries. There is nothing to do except try to get a refund from the eBay seller and then get a real Motorola OEM battery from a more reputable seller. I also suggest you complain directly...