Let me use an analogy here.
Lets say your computer is a car, and you want to know how to fix your car....but you are NOT a mechanic.
So, what do you do?
Learn to become a mechanic, so you can fix your car on your own...or....
take your car to a mechanic to get it fixed.
Now, your car isn't exactly BROKEN persay.....rather it is getting broken INTO, just as a car would....somebody keeps getting into your car. and snooping around.
So what do you do.....put a car alarm on it, and hope for the best.
The same scenario aplies here.
All you are essentially doing is putting a computer alarm on your computer. This is done with MONITORING tools.
These tools are usually NOT free, and can be VERY expensive, as they are VERY VERY in-depth, and are designed for the ENGINEER to use, not a novice computer user.
So, what are your choices?
Install and get frinedly with the monitoring tools yourself....which is ultimately the best thing.
take it to a computer shop, and explain what is happening, and have them install monitoring software on it, and take you through a TEST drive, to show you some of the basics.
I woudl reccommend ORION SOLARWINDS as the software of choice. They have many different types of monitoring, and can also PREVENT intruders to the network. But, everything comes with a cost.
Heres the link to find out more.