My laptop (inspiron 1520) is around 4 years old and started getting slower a couple months ago.

 

I found the cause by using speccy.

 

My laptop has 2 cores and the stock core speed for each one is 1466 MHz

 

But now, each core is running at half the speed around 779 MHz making my computer a whole lot slower.

 

How can I fix this?

 

I've already gone through a whole system restore (deleting all the files and restoring to factory settings)