Cannot boot to Windows

IIm working on a PC that I donnot have a recovery disk for. It boots all the way to the windows screen then attempts to fix itself and never does. It keeps going into a repeatitive motion never booting fully to windows. I have tried all the function keys and I cant get it to go into safemode. I have a copy of BootMed that I tried but now its saying selected boot device is unavailable. H...E...L...P!!!

First of all can you tell us what is the operating system installed on your machine? What is the full computer specifications that you have? Also, you will need to download and burn a BootMed to a cd or dvd. After that you have to go into bios and select first booting options to cd/dvd drive and restart the computer. After restart follow the procedures to restore the windows OS again.