Wierd thing happend

Hello, so something very wierd happend with my computer and i'd like to ask why that happend.
So, I was downloading youtube videos to my computer and I was adding them into iTunes. I have to mention that I was un-installing and installing some programs ( installed and uninstalled like 3-4 times) and after that i noticed my computer is wierd a bit, checked for any problems, ran SpeedUpMyPCand and many more programs to fix problems hidden in your computer. After that I had to restart my PC, here wierd thing pops up. I retarted it normally, windows was running normally, showed my desktop, and everything changed. My shortcuts were missing, desktop (theme) was like I just installed Windows, but all programs are installed, wierd thing, so im asking you, why this happend?
Is it cuz i installed and uninstalled too many times 1 thing?. or what caused this?

thanks in advance!