how to re-hide system folders in finder?

background: A while back I had a bit of trouble with my computer and I had it repaired at a local applestore. the computer worked fine for a while but has been acting up and running slow lately(poor baby is getting old and might be due for a replacement soon, but am not ready to part with her quite yet...) all of a sudden yesterday all the hidden systemfiles showed up in my finder window.

Current problem: I've already tried all the different "com.apple.finder..." commands in Terminal from this and other forums, but just comes up with "command not found"

I found a reply here that said I could go and delete the com.apple.finder file in Library preferences -

then what I found was this: for some reason I do not have an com.apple.finder plist file in my library..

I have not deleted it myself. what might be the reason for this? all hidden files are now shown in my finder windows to my frustration making every file I have to find a tiresome task, and my favourites keep disappearing from the sidebar(not sure if this is a connected problem, but has been going on longer than the hidden files).

Any help with this would be much appreciated.