Read old Action logs? client security

Hello, 

I am a high school student and have not a lot of knowledge about internet security.

I have a question about Old action logs or invaded.

I feel my PC was stranger three days ago, invaded by someone ? and get my privacy data...

I want to know if my PC has been invaded or not? has been set a backdoor or not.

How can I check it?

I try to check the action log of my F-secure client on that day, but it has gone.

I want to know the log at 18:20, but the last is 19:12.

The introduction about action log:

The action log is collecting data about the actions done by the firewall continuously. It is a normal text file with the maximum size of 10 MB, and can be viewed with any text editing application capable of reading large files. The action log file can be cleared and removed anytime, so it is easy to restart into a new file if the file size gets too big. You can view the action log by clicking Show Action Log on the Logging page.

my security level is office! (Windows 8.1)

this is my earlier log, show as below:

2015-12-05T19:12:28+09:00,info,appl control,C:\  

I want to know more early, how can I do that...   help please.