If it's happening almost immediately, I am wondering if you used too little paste or it's not seated correctly. What you describe, about a dime, is usually correct. If the “sandwich" of processor - paste - heat sink has any gaps, especially above the hotter parts of the processor, then no heat is getting transferred and it would certainly bug out rather quickly.
The most universal way to reset a bios password is to unplug the CMOS battery. It usually looks like a little coin battery with two wires coming out of it, just unplug it for say, I dunno, a minute or so and plug it back in. This should clear the password (and everything else in the bios will go back to defaults so make sure to adjust stuff back you've made any tweaks)
What you're looking for is called a standoff screw, if that helps any. Also it's not great but you should be able to use the phone just fine without it. Use an organizer next time to keep better tab of your parts.
According to the Dell support website, five beeps is indicative of a bad CMOS battery. Usually this is just a 2032 coin with leads soldered to it and should be cheap enough to pick up. That said, verify the number of beeps as even one less can mean something completely different. https://www.dell.com/support/article/us/...-xps-18-understanding-diagnostics-and-beep-codes?lang=en
Try different sized flathead screwdrivers. Also try pulling up on the component being held down slightly as you turn it, this can hopefully help move it around a bit more and give it something to push back
You don't seem to have uploaded an image so it's a little hard to tell, but according to the guide they should just be regular Phillips head screws. It's possible they got stripped if too much torque was applied, can you try uploading or linking an image again?
It shouldn't make a difference, my bigger concern is the quality of the product between the two and not so much the write speed. I sincerely doubt you will notice any major difference between the two so if you consider them both a quality product, go with the cheaper one.
It still thinks that it's open. Check the switch again, make sure everything is wired correctly. Also make sure that whatever contact is being made when the door is being closed is actually being made; if the door closes funny after installing the new switch then you'll need to go back and figure out why it isn't seated all the way in.
Have you tried opening a browser? Usually with these cases you are required to login some other way besides using just the Wifi password, especially at a school. Check with your front office, they probably have the login information (unless it's not actually a guest account for students, in which case you're probably out of luck by normal means)
It's fine. You can usually buy 91% in any store that sells 70% and that would be better (99% is available online as well) and less water is always better. That said, “rust" is not the issue as it will evaporate fairly quickly; don't power on the device until all of the alcohol has evaporated as you don't want any liquid getting sucked into the device.