When My friend got his first computer a PC I used to get support calls from him (about 8-9 years ago)
"hey man my computer has stopped working!!"
"What were you doing at the time?"
"I was removing some programs I don't use"
"ok like what"
"well I was in the windows directory and I deleted some .exe programs I don't use calc.exe etc"
"Ok any thing else?"
"Yeah there were this files with .dll extension what wouldn't execute and they were taking up so much space so I deleted them and freed up so much space but now my machine won't reboot.!!!"
Well when I stopped laughing I told him just to re install the machine.
I havn't stopped teasing him either about it

I will admit when he reinstalled his machine every other day he now knows a lot more