Formating pc problems?

put format disc in, tells me which operating system, cannot use keyboard, then starts loading(without disc in) and comes up " the file iastor.sys could not be found , press any key to continue,cannot as keyboard wont work, i turn it off without disc in again and comes up again , pc was working fine til then , just wanted to format the hard drive and this happens, restart again F8 and ide-0 and return, same thing (windows setup) stops again as above, start through cd rom(no cd in) and comes up with the same, so every time i turn it on it tries to format the hard drive with no format disc in , PLEASE HELP , wish i didnt try to format the disc