Clean Start or resetting Mathematica‘s preferences ?

Questions
,
1

My Mathematica {10.1} is acting quite “odd”, in a manner of speech. Long ago someone told me how to flush the system. I think he called it a clean start. If anyone can help me with this, I would be forever grateful.

2

I think this is what you are looking for:

How do I fix common problems by resetting Mathematica to its default configuration?

3

thanks, I’ll send you $1000. I kid.