Sounds like you need a new power button. Part no Ls-a991p will get you the button and the cable.

Iso wipes or using the alcohol on a soft towel is OK to use. If you find that the wipes don't clean it good enough dawn and water on a soft towel with very light rubbing will do it. As you long as you lightly rub/wipe it the paint won't come off. Tip:Don't use bathroom towels. Microfiber is your friend here.

This error contains lots of reasons. The first and easiest is to open the ink door and remove the cartridges and put them back in and close the door. Replace any ink cartridge that feels or sounds empty. Unplug all cords to the printer except the power cord. Turn it off and on then hold down the go button for 10 seconds. This will reset it to factory defauts.

As you know there is an issue with the play store. Reset it by going to Settings > Application Manager > Google Play Store > Disable. Then turn it back on by clicking Enable. If this doesn't fix it then you will have to restore the device to the factory image.

That cable assembly has a part number similar to 821-1609-03. Remove the entire assembly and search the Internet for that part number and you'll be good to go.

You have two things going against you. 1. Your CPU being a Celeron will always be a slow point on your computer. 2. Your drive slows down as it ages. This doesn't mean your drive is dying it just happens. First use memtest to ensure your RAM's integrity. If that passes, There are two things you can do. 1. Replace your drive by cloning it over to a new one or installing fresh from CD or USB. 2. Using a different computer to low level format your drive and install the OS from CD or USB.