Okay well I uninstalled a bunch of unneeded programs, it didn't free up that much space really, in the end I freed about a gigabyte or so... I keep my program list clean, and as you can see on this screenshot
I pretty much need all of those programs for something. All the games
products you see are heavy programs and are thus installed on a completely different hard drive, just so you know.
I still don't get why the compress old files function is not available in disk cleanup however. I'll try your defrag tool you suggested now.
Update: Okay, I used the defragmenter. It tells me my speed increased by +4% now. Also it says in red letters "Warning: Your PC is not optimized". It recommends I download Auslogics BoostSpeed to improve the performance of Windows Core, Internet Browser, Disks and Registry. Should I do this? And how did the defrag process really help me besides just speeding up my system a little?
I still wanna find out what happened to my Compress Old Files function though.