I had something similar last week. We - by that I mean Peter next door - finished up by wiping every single thing from the hard drive using some special utility he downloaded from somewhere. Hard drive had nothing at all on it. Had to rebuild from scratch, re partition, install all the hidden techy bits that only anoraks know about, then put all the drivers back on. Only then could Windows go back on. Seems like hard drive had become corrupted way down deep in the works. Peter reckoned that a repair shop would have just ditched the drive and sold me a new one. Saved me a small fortune. In fact if it had gone to a shop it would probably have been more economical to ditch it and buy a new one.
You could do with finding a Peter!!!