every few days i come home 2 find i have lost a few gig off my hard drive but can not find what has been saved to it is there a way to find out

Every few days i come home to find i have lost a few gig off my hard drive but can not find what has been saved/installed to my hard drive is there a way to see everything that has been saved to my hard drive in the last few days i am using windows 7 internal hard drive

I have tried cheaking my installed programs to see if any one has been installing new programs without my consent and there are no new installs

I have gon threw my existing programs to see what info they are saving to my hard drive and it does not account for the amount i am loosing

I have come to the conclusion that some one is useing and saving infomation to my hard drive or a hacker has got in to my pc and using it for storeg or as extra processing power and space to run a programs