r u sure that u can't start with safe mode or A drive(u have to press F8 while starting, after finishing the memory exam)?if the answer is yes do following.
take off ur hd from ur pc,borrow an hd from some1 else to start the pc and put ur hd on the secondary master. install software on ur friends' hd to support double hd in 1 pc. and ........................do whatever u want to backup, then format and reinstall. after reinstalled, if the problem remains, then u might have to change ur hd or else u can try low format(repartition, retrack, etc)