Assuming the charger, port and cable are all okay, then it sounds like a completely dead battery. Presumably it is a secondhand item and several years old, though you have only recently acquired it. The seller may have got rid of it for this reason. The good news is that replacement battery kits (including the tools) are easy and cheap to get and if you or a friend are up for it, it takes less than an hour to install. Start with a clean table, small pots and tape to keep track of the screws and a good strong light to work by. We did this for my son's iPhone 5 and it came back to life like a new one and is still going strong more than a year later.
I assume you mean 'I do NOT have Applecare'? It is annoyingly expensive but often worth it for mobile devices as you have found out. Anyway, you are lucky the phone is still working. I would follow an fixit guide to take the case apart, remove the larger components and let it dry out naturally for a longer period, but another old trick is to put it in a container of rice and leave it there for several days where the rice will gently absorb moisture. A Canon EOS camera of ours was completely(though briefly) submerged last year, but came completely back to life after a couple of weeks 'in the rice'.
A good approach is to follow ifixit guides slowly and carefully, studying the photos and making sure you reassemble using the right parts in the right places. I have replaced a couple of iPhone batteries and it is quite do-able, but extremely fiddly and quite easy to get something wrong for example with the small ribbon press connectors. If you go back and do it again, you may be lucky and find that the screen connection wasn't made well and it may burst back into life. On the other hand, you may have caused some damage along the way, which will need another fix.
It's most likely the batteries have completely discharged in the cold. Most likely, once the Kindle is back up to room temperature you can plug it in to the charger and it will eventually wake up. There are no moving parts in the Kindle to be affected by cold!
The iMac logic board is pretty picky about the thermal sensors it recognises and will go into general fan panic if in doubt. Do all your upgrade items have compatible sensors and are they all connected properly? OWC are pretty up to speed on this and may have guidance.
It does sound like a hardware problem. I had similar issue and Apple replaced the logic board entirely - though that's their solution for many problems. It's quite interesting to use a USB Multimeter which plugs into your USB port and looks at volts, amps, and tests charging voltage & current. CoJoie make a good one, but many other options on Amazon.
Crucial.com offer multiple options for maxing out RAM and SSD's. If you access the site from the laptop you wish to upgrade, it will offer to automatically run diagnostics and tell you exactly what's possible. I have used their components in several Macs and never been disappointed. Having said that, the problem of 'slowing down' seems to happen with age and the accretion of files and junk. I quite like utilities like Clean My Mac, but many others don't, and it can be overenthusiastic in its actions. Once every couple of years it's worth copying your user accounts off, wiping the startup disk, reinstalling the OS, reinstall only the applications you actually use, steer clear of 3rd party utilities and enhancements, import your user account and it's like the machine when it was new. Received wisdom is that you shouldn't need to do this, but the speed bump is undeniable. A lesser, but still effective route can be to start up from the Recovery partition and reinstall the system, create a new user account and...
Hi, It's definitely worth gently extracting any dust and fluff from the back of the Mac and the fan. As far as I know you can't swap out the processor PC-style. You might have a look at TG Pro from TunaBelly software which will offer you some useful monitoring and where you can boost the fans in case of overheating. But, their notes would say that 85deg. while high, is not excessive. Specifically, from their monitoring advice: Green - The temperature is between 0 to 89C (32 to 192F) and is generally nothing to worry about Orange - The temperature is between 90 to 99C (194 to 210F) and is getting closer to the thermal limit of the hardware. Red - The temperature is at or above 100C (212F) and it very close to the thermal limit. It's a good rule to not let components run this hot for an extended period of time. It's usually a CPU sensor that will display a temperature this high. Most of the Intel CPUs have a maximum of 95C (203F) to 105C (221F) at which point they will slow down to avoid damage. Hope that helps