Solved Sudden decrease of ~5GB in free space in C:

Hello, I recently noticed that my drive C: decreased in around 5GB. I have my HDD partitioned in 2 (100GB for C: and 350GB for D:), and I store everything in drive D:. I have kept my drive C: with around 30.5GB of free space for several months now, but since last week that suddenly dropped to 24.8GB. I checked with WinDirStat, which shows that C: does have 69.5GB in use. I don't know if this...