I was downloading stuff from gyanche to have a messenger application. But it did not work. I turned off my pc. When I turned it on again, it says that i have to repair installation. the thing is, i can’t remember what the files were, i dont know where to find it to delete it or repair it. so im sooo stuck. 
pop in your cd/dvd & boot from it,then,select the repair option
Andy
As per Andy’s comment. Probably choose the automatic option in repair if you are a little unsure.
Just guessing here, as I have never used repair- but watch it doesn’t change the bootloader from your current setting.