Firstly - Why are you messing arround with attributes?
Secondly - Why did you apply the attributes to everything in C?
Your command basically says..
for all files and folders in C: remove
the attribute System File, Read Only and Hidden.
Different files and folders have different attributes set so you're stuff in terms of getting them back to "default". What you have run, you've basically done a "show all".
I would first try going to Control Panel > Folder Options/File Explorer Options > View > Restore Defaults
If you swap the - for a + in your command you will do the reverse operation.
attrib +H C:\test would add the hidden attribute to the folder and it would become hidden.