What version of windows are you using? XP and Vista both have recovery options (Vista more specifically targeted at startup issues). You should be able to boot off the OS CD's to gain access to these options.
It is my sisters computer and she has windows 95. She has no books or boot disc. I downloaded one but it would not run. When the computer starts it flashes quick to winows 95 then goes to the screen that gives you choices to start but I don't do dos. All I have is the windows 95 disc which does nothing.
I replied to your thread earlier without reading this one. If you have the disk then try booting up from that disk and see if it gives the option of repair install, if not then I d say there is not other option but to reinstall the whole OS. But before that I d say you should get the data backed up by connecting the hard disk to another pc as slave and copy the data. Atleast your data would be safe.