Q&A for How to Clean Your Computer System

Try CCleaner. If you need to remove a load of apps and you think they may have external files (such as /Library/Application Support), try AppCleaner. In addition, it can help to look through the following directories and check for files belonging to old apps. Directories are: /Library/ (be careful!) /Library/Application Support/ /Library/Internet Plug-Ins/ /Library/LaunchDaemons/ /Library/LaunchAgents/

No, you cannot. Hard drives are electronic and have moving parts. If you do try to clean it with water, the drive will most likely fail.

If you can't get it to run in safe mode you need to restore your computer to factory settings. Unfortunately, you will lose all of your files and any apps you have installed.

Yes, as long as you dry it off with a hair dryer or something like that afterward. Make sure you remove it first.

It's enough to remove your GPU (graphics) and your CPU-fan. With a thin vacuum head, you should be able to clean all spots thoroughly. For the hard-to-reach spots, you can "blast" the dust with your hair dryer. Be careful when using a brush to not scratch the main-board.