my computer is running ok it seems except for the fact i cant defrag just now because my c drive is saying its full and theres not enough space to use the defrag program , so now im having a hard time wondering what files i should delete on my c drive.

i keep using c cleaner to clean the registry but ive never backed anything up, my computer continues to operate ok, could i have done anything harmful to the computer ? would i know if i had ?

alsoo a user said this in my last question in response to not being able to defrag my c drive :

” There is a thing where you can buy in stores and you plug it into your computer and stor everything on it. Then delete the things on your computer you can take it where ever you go and have your work ”

has anyone heard of a gadget like hes describing ?

my operating system is windows xp btw, i cant afford vista right now.